DEllorto carbs
04-02-10, 12:37 PM
#1
DEllorto carbs
Well, since I'm having to jump through so many hoops to get help and info on the Dellorto carbs, I decided to start this thread to condense all the info and help I can find/get into one place so maybe it will help some others later too. Also, FYI to the current Dellorto guys and those who are considering purchasing one. I just got hooked up with a guy in AZ that is setting up to be a "distributor" of Dellorto stuff, so getting parts doesn't need to be done through AUS, or Itally now. 
If anyone has any specific or general info about anything from jetting to model info on these, feel free to post it. It's very helpful to have all the info in one spot.
Ray
If anyone has any specific or general info about anything from jetting to model info on these, feel free to post it. It's very helpful to have all the info in one spot.Ray
04-02-10, 12:55 PM
#2
Selection and tuning
Selection and tuning of Dellorto DHLA carburettors
A very popular modification for RX7 owners is the fitment of twin Dellorto DHLA, these carburettors are very similar to the Weber DCOE range and not only deliver the goods but also look very good. A good deal of mystique surrounds Dellortos, specifically jetting and tuning. However Dellorto DHLA series carbs are not as complicated as you might imagine, and whereas there is no substitute for a good rolling road session to tune them, there is much you can do to tune them yourself, by selecting the correct choke sizes and initial jet settings according to a fairly simple set of rules. This should get the engine running to a reasonable standard in preparation for the rolling road.
Arriving at the correct carb/venturi size
When selecting Dellortos, the most commonly asked question is "Should I have 40s or 45s" coupled with "Surely the 45s will give more power". This shows a basic misunderstanding of the construction and principles of operation of the DHLA series. It is not the barrel size (40 or 45) which determines the airflow and therefore potential horsepower; it is the size of the main venturi or choke. Selection of the correct main venturi size is the first step in selecting the carburettor.
It is easy to make the assumption that biggest is best when selecting a main venturi size, but the purpose of the main venturi is to increase the vacuum acting on the main jet in order to draw in and effectively atomise the fuel mixture. The smaller the main venturi, the more effective this action is, but a smaller venturi will inhibit flow. A large venturi may give more power right at the top end of the power band, but will give this at the expense of lower RPM tractability. Only a circuit racer will benefit from this sort of compromise, on a road car, driveability is much more important. 95 percent of the time, a road engine is nowhere near its peak power, but is near its peak torque for 75 percent of the time. It is much more important therefore to select the main venturi for best driveability, once the venturi size has been selected, then the appropriate carburettor size can be arrived at.
Here is a small chart showing the available Main Venturi size for Common DHLA series carbs
Size Available Venturi sizes
40 24-36mm
45 28-40mm
48 40-43mm
Below is a chart that will allow the correct selection of main venturi size for engines given the engines capacity and the RPM at which peak power is realistically expected to be achieved, for road engines peak power is usually between 5250 and 6500, depending on the cam selection. After the correct venturi size has been arrived at it is a simple matter to determine whether 40/45 or 48 DHLAs are required, take the venturi size and multiply by 1.25, the result is then the ideal barrel size which will accommodate the venturi size selected.
Carburettor Barrel size calculation
Venturi/choke size * 1.25
For example: a two litre engine giving its maximum power at 6000RPM will require a venturi size of 36mm, and therefore an ideal barrel size of 45mm (36 * 1.25), for this application 45 DHLA is the ideal solution. However a 40 DHLA will accommodate a 36mm choke, so if funds are limited and the engine is not going to be tuned further then 40 DHLAs will do the job.
If you have bought your Dellortos second-hand, it is important to understand that it is unlikely that they will be 'ready jetted’. However if you do not want the expense of changing the main venturis, you will still need to know their size, this is normally embossed on the venturi itself, so look carefully down through the main barrel of the carb from the air cleaner side.
Main Jet and Air Corrector Size Selection
A useful formula for the calculation of main jet size when the main venturi size is known is to multiply the main venturi size by 4. This will give a starting point for the main jet size which should be 'safe', again as a starting point the emulsion tubes can be selected from the table shown below, although for Pinto 7772.7 or 7772.6 will generally be OK. If your carbs are already equipped with these, then that will save you some money. Air corrector jet initial settings should be around 50 higher than the main jet.
Main jet size Venturi size * 4
Air corrector Main jet size + 50
Using these formulae, a venturi size of 36mm will require a main jet of 145 and an air corrector of around 190.
Emulsion tube Selection
Below is a table showing suggested emulsion tube type, for a given single cylinder capacity.
Cylinder capacity Suggested tube
250-325 7772.8
275-400 7772.7
350-475 7772.6
450-575 7772.5
Using the above formulae, the ideal settings for a 2000cc Pinto with power peaking at 6000RPM (290 degree cam or above) are as follows
36mm chokes
7772.6 or 7772.5 Emulsion tubes
145 Main jet
190 Air corrector
The 2000cc Pinto in just on the cusp of change for emulsion tube type between 7772.6 and 7772.5, if you already have 7772.6 tubes, use them it is not worth the expense of change, they will just cause the main circuit to start marginally earlier. A 2.1 or 2.2 Pinto should however be using 7772.5s although 7772.6s will do the job acceptably well.
Idle Jet selection
Idle jets cause a lot of confusion; although their name suggests that they govern the idle mixture, this is incorrect. It is true that the fuel consumed at idle is drawn through the idle jet, but the idle mixture is metered not by these jets, but by the idle volume screws mounted on top of each barrel. The idle jets control the critical off-idle progression between closed throttle and the main jet circuit, it is this part throttle operation which is so important to smooth progression between closed throttle and acceleration and for part throttle driving. If this circuit is too weak then the engine will stutter or nosedive when opening the throttle, too rich and the engine will hunt and surge especially when hot. The technique for establishing the correct idle jet size is detailed later, but as a starting point 40/45 7850.2 idle jets for a 1600 engine 45/50 7850.2 for an 1800 and 50/55 7850.2 for a 2000 will get you out of jail free.
Below is a chart showing approximate idle jet sizes for given engine sizes, this assumes one carb
barrel per inlet port E.G. two DHLAs.
Engine size Idle jet size
1600cc 40/45
1800cc 45/50
2000cc 50/55
2100cc 55/60
Establishing the correct idle jet for a given engine is not easy but usually an approximation will make the car acceptably driveable. If the progression is weak then the engine will nosedive when moving the accelerator from smaller to larger throttle openings. A certain amount of change (richer/weaker) to progression can be achieved by varying the idle air jet holder size; this alters the amount of air, which is emulsified with the fuel drawn through the idle jet. If this does not richen the progression sufficiently then the next jet size up, with the same air bleed should be tried. Below is a small chart showing the most commonly used air size designations, running from weak to rich. Generally speaking start your selection with a 7850.2 air bleed.
Weaker Normal Rich
7850.5 .10 .9 .4 .1 .3 .6 .7 .2 .8
The ones in normal use are 7850.1, 7850.6 , 7850.2 and 7850.8.
Setting the Idle and slow running
Rough running and idle is normally down to the idle mixture and balance settings being incorrect, below is a technique to establish a clean idle and progression. Before adjusting the carbs in this manner you must make sure that the following conditions are met.
i) The engine is at normal operating temperature
ii) That the throttle return spring/mechanism is working OK
iii) That the engine has sufficient advance at the idle speed (between 12 and 16 degrees)
iv) That an accurate rev counter is connected.
v) That there are no air leaks or electrical faults.
A reasonable idle speed for a modified engine on Dellortos is between 900 and 1100 RPM.
If you are adjusting the idle for a set of carbs already fitted then progress to the second stage. If the carbs are being fitted for the first time, screw all of the idle mixture adjustment screws fully home and then out 2.5 turns. Start the engine and let it reach normal operating temperature. This may mean adjusting the idle speed as the engine warms up. Spitting back through the back of the carburettor normally indicates that the mixture is too weak, or the timing is hopelessly retarded. If this happens when the engine is warm and you know that the timing is OK, then the mixture will need trimming richer on that cylinder. Set the idle as near as you can to 900RPM.
Using an airflow meter or carb synchroniser adjust the balance mechanism between the carbs to balance the airflow between them, if the rearmost carb is drawing less air than the front, turn the balance screw in a clockwise direction to correct this. If it is drawing more air, then turn the balance screw anti-clockwise. If the Idle speed varies at this point adjust it back to 900 RPM, to decrease idle speed screw in an anti-clockwise direction, to increase, screw in a clockwise direction.
When you are sure that the carbs are drawing the same volume of air, visit each idle mixture screw, turn the screw counter clockwise (richening) in small increments (quarter of a turn), allowing a good 5 - 10 seconds for the engine to settle after each adjustment. Note whether engine speed increases or decreases, if it increases continue turning in that direction and checking for engine speed, then the moment that engine speed starts to fall, back off a quarter of a turn. If the engine speed goes well over 1000RPM, then trim it down using the idle speed screw, and re-adjust the idle mixture screw. If engine speed decreases then turn the mixture screw clockwise (weakening) in small increments, again if engine speed continues to rise, continue in that direction, then the moment it starts to fall, back off a quarter a turn. The mixture is correct when a quarter of a turn in either direction causes the engine speed to fall. If that barrel is spitting back then the mixture is too weak, so start turning in an anti-clockwise direction to richen. During this procedure, the idle speed may become unacceptably high, so re-adjust it and repeat the procedure for each carb barrel.
After all the mixture screws have been set, the idle should be fairly even with no discernible 'rocking' of the engine, if the engine is pulsing, spitting or hunting then the mixture screws will need further adjustment. If the engine is rocking or shaking then the balance is out, so revisit with the airflow meter/ carb synchroniser. No amount of adjustment will give a good idle if the throttle spindles are bent or leaking air or the linkages are loose on the spindles!
That’s all there is to it.
Starting technique for Dellorto equipped engines (engine cold)
Some Dellortos have a cold start circuit (choke), others don't, in my experience, it is very easy to flood the engine and wet plugs using the cold start mechanism, as it very crude in operation. The accepted technique for cold starting is as follows:-
Allow the float chambers to fill if you have an electric pump, this should take about 5-10 seconds, fully depress the accelerator rapidly four times, then on a light throttle, turn the engine over, if it does not start immediately, repeat the procedure three times. The engine should fire, but may need 'nursing' for a minute or two before it will idle, gentle prodding of the accelerator should keep it alive long enough for it to warm up. If the engine does not fire within three attempts, then try five or six pumps. If this does not work, depress the accelerator fully and hold it open while turning the engine over for 5 to 15 seconds, then close the accelerator and try again.
Buying second-hand
When buying Dellortos second-hand ensure that they are a matched pair. Look carefully at the serial numbers on the top of the carbs, these should be the same, or very similar. If they are not then they are not a matched pair and may well give problems when trying to jet them, as the progression drillings could be different. Inspect the carbs very carefully before parting with your cash, check their general condition, check for fire/heat damage, check that the butterflies open and close smoothly and that the linkages are smooth in operation and the carbs don't stick open. A common problem with Dellortos is the attachment of the throttle quadrant to the spindle, these can wear and will give an erratic idle and progression which no amount of tuning will cure. It is important to note that Dellortos are very rarely 'ready jetted' so factor the cost of jets etc. when deciding on your purchase. Check the throttle spindles for wear, excessive wear here will bleed air into the engine and again will affect setting up dramatically. Servicing kits for Dellortos are relatively cheap so a neglected pair, provided that the above checks are carried out, can be restored to very good condition by a thorough clean and service, the servicing is not difficult but has to be done in a clean environment, using a methodical approach.
Credit to Dave Andrews for above info
A very popular modification for RX7 owners is the fitment of twin Dellorto DHLA, these carburettors are very similar to the Weber DCOE range and not only deliver the goods but also look very good. A good deal of mystique surrounds Dellortos, specifically jetting and tuning. However Dellorto DHLA series carbs are not as complicated as you might imagine, and whereas there is no substitute for a good rolling road session to tune them, there is much you can do to tune them yourself, by selecting the correct choke sizes and initial jet settings according to a fairly simple set of rules. This should get the engine running to a reasonable standard in preparation for the rolling road.
Arriving at the correct carb/venturi size
When selecting Dellortos, the most commonly asked question is "Should I have 40s or 45s" coupled with "Surely the 45s will give more power". This shows a basic misunderstanding of the construction and principles of operation of the DHLA series. It is not the barrel size (40 or 45) which determines the airflow and therefore potential horsepower; it is the size of the main venturi or choke. Selection of the correct main venturi size is the first step in selecting the carburettor.
It is easy to make the assumption that biggest is best when selecting a main venturi size, but the purpose of the main venturi is to increase the vacuum acting on the main jet in order to draw in and effectively atomise the fuel mixture. The smaller the main venturi, the more effective this action is, but a smaller venturi will inhibit flow. A large venturi may give more power right at the top end of the power band, but will give this at the expense of lower RPM tractability. Only a circuit racer will benefit from this sort of compromise, on a road car, driveability is much more important. 95 percent of the time, a road engine is nowhere near its peak power, but is near its peak torque for 75 percent of the time. It is much more important therefore to select the main venturi for best driveability, once the venturi size has been selected, then the appropriate carburettor size can be arrived at.
Here is a small chart showing the available Main Venturi size for Common DHLA series carbs
Size Available Venturi sizes
40 24-36mm
45 28-40mm
48 40-43mm
Below is a chart that will allow the correct selection of main venturi size for engines given the engines capacity and the RPM at which peak power is realistically expected to be achieved, for road engines peak power is usually between 5250 and 6500, depending on the cam selection. After the correct venturi size has been arrived at it is a simple matter to determine whether 40/45 or 48 DHLAs are required, take the venturi size and multiply by 1.25, the result is then the ideal barrel size which will accommodate the venturi size selected.
Carburettor Barrel size calculation
Venturi/choke size * 1.25
For example: a two litre engine giving its maximum power at 6000RPM will require a venturi size of 36mm, and therefore an ideal barrel size of 45mm (36 * 1.25), for this application 45 DHLA is the ideal solution. However a 40 DHLA will accommodate a 36mm choke, so if funds are limited and the engine is not going to be tuned further then 40 DHLAs will do the job.
If you have bought your Dellortos second-hand, it is important to understand that it is unlikely that they will be 'ready jetted’. However if you do not want the expense of changing the main venturis, you will still need to know their size, this is normally embossed on the venturi itself, so look carefully down through the main barrel of the carb from the air cleaner side.
Main Jet and Air Corrector Size Selection
A useful formula for the calculation of main jet size when the main venturi size is known is to multiply the main venturi size by 4. This will give a starting point for the main jet size which should be 'safe', again as a starting point the emulsion tubes can be selected from the table shown below, although for Pinto 7772.7 or 7772.6 will generally be OK. If your carbs are already equipped with these, then that will save you some money. Air corrector jet initial settings should be around 50 higher than the main jet.
Main jet size Venturi size * 4
Air corrector Main jet size + 50
Using these formulae, a venturi size of 36mm will require a main jet of 145 and an air corrector of around 190.
Emulsion tube Selection
Below is a table showing suggested emulsion tube type, for a given single cylinder capacity.
Cylinder capacity Suggested tube
250-325 7772.8
275-400 7772.7
350-475 7772.6
450-575 7772.5
Using the above formulae, the ideal settings for a 2000cc Pinto with power peaking at 6000RPM (290 degree cam or above) are as follows
36mm chokes
7772.6 or 7772.5 Emulsion tubes
145 Main jet
190 Air corrector
The 2000cc Pinto in just on the cusp of change for emulsion tube type between 7772.6 and 7772.5, if you already have 7772.6 tubes, use them it is not worth the expense of change, they will just cause the main circuit to start marginally earlier. A 2.1 or 2.2 Pinto should however be using 7772.5s although 7772.6s will do the job acceptably well.
Idle Jet selection
Idle jets cause a lot of confusion; although their name suggests that they govern the idle mixture, this is incorrect. It is true that the fuel consumed at idle is drawn through the idle jet, but the idle mixture is metered not by these jets, but by the idle volume screws mounted on top of each barrel. The idle jets control the critical off-idle progression between closed throttle and the main jet circuit, it is this part throttle operation which is so important to smooth progression between closed throttle and acceleration and for part throttle driving. If this circuit is too weak then the engine will stutter or nosedive when opening the throttle, too rich and the engine will hunt and surge especially when hot. The technique for establishing the correct idle jet size is detailed later, but as a starting point 40/45 7850.2 idle jets for a 1600 engine 45/50 7850.2 for an 1800 and 50/55 7850.2 for a 2000 will get you out of jail free.
Below is a chart showing approximate idle jet sizes for given engine sizes, this assumes one carb
barrel per inlet port E.G. two DHLAs.
Engine size Idle jet size
1600cc 40/45
1800cc 45/50
2000cc 50/55
2100cc 55/60
Establishing the correct idle jet for a given engine is not easy but usually an approximation will make the car acceptably driveable. If the progression is weak then the engine will nosedive when moving the accelerator from smaller to larger throttle openings. A certain amount of change (richer/weaker) to progression can be achieved by varying the idle air jet holder size; this alters the amount of air, which is emulsified with the fuel drawn through the idle jet. If this does not richen the progression sufficiently then the next jet size up, with the same air bleed should be tried. Below is a small chart showing the most commonly used air size designations, running from weak to rich. Generally speaking start your selection with a 7850.2 air bleed.
Weaker Normal Rich
7850.5 .10 .9 .4 .1 .3 .6 .7 .2 .8
The ones in normal use are 7850.1, 7850.6 , 7850.2 and 7850.8.
Setting the Idle and slow running
Rough running and idle is normally down to the idle mixture and balance settings being incorrect, below is a technique to establish a clean idle and progression. Before adjusting the carbs in this manner you must make sure that the following conditions are met.
i) The engine is at normal operating temperature
ii) That the throttle return spring/mechanism is working OK
iii) That the engine has sufficient advance at the idle speed (between 12 and 16 degrees)
iv) That an accurate rev counter is connected.
v) That there are no air leaks or electrical faults.
A reasonable idle speed for a modified engine on Dellortos is between 900 and 1100 RPM.
If you are adjusting the idle for a set of carbs already fitted then progress to the second stage. If the carbs are being fitted for the first time, screw all of the idle mixture adjustment screws fully home and then out 2.5 turns. Start the engine and let it reach normal operating temperature. This may mean adjusting the idle speed as the engine warms up. Spitting back through the back of the carburettor normally indicates that the mixture is too weak, or the timing is hopelessly retarded. If this happens when the engine is warm and you know that the timing is OK, then the mixture will need trimming richer on that cylinder. Set the idle as near as you can to 900RPM.
Using an airflow meter or carb synchroniser adjust the balance mechanism between the carbs to balance the airflow between them, if the rearmost carb is drawing less air than the front, turn the balance screw in a clockwise direction to correct this. If it is drawing more air, then turn the balance screw anti-clockwise. If the Idle speed varies at this point adjust it back to 900 RPM, to decrease idle speed screw in an anti-clockwise direction, to increase, screw in a clockwise direction.
When you are sure that the carbs are drawing the same volume of air, visit each idle mixture screw, turn the screw counter clockwise (richening) in small increments (quarter of a turn), allowing a good 5 - 10 seconds for the engine to settle after each adjustment. Note whether engine speed increases or decreases, if it increases continue turning in that direction and checking for engine speed, then the moment that engine speed starts to fall, back off a quarter of a turn. If the engine speed goes well over 1000RPM, then trim it down using the idle speed screw, and re-adjust the idle mixture screw. If engine speed decreases then turn the mixture screw clockwise (weakening) in small increments, again if engine speed continues to rise, continue in that direction, then the moment it starts to fall, back off a quarter a turn. The mixture is correct when a quarter of a turn in either direction causes the engine speed to fall. If that barrel is spitting back then the mixture is too weak, so start turning in an anti-clockwise direction to richen. During this procedure, the idle speed may become unacceptably high, so re-adjust it and repeat the procedure for each carb barrel.
After all the mixture screws have been set, the idle should be fairly even with no discernible 'rocking' of the engine, if the engine is pulsing, spitting or hunting then the mixture screws will need further adjustment. If the engine is rocking or shaking then the balance is out, so revisit with the airflow meter/ carb synchroniser. No amount of adjustment will give a good idle if the throttle spindles are bent or leaking air or the linkages are loose on the spindles!
That’s all there is to it.
Starting technique for Dellorto equipped engines (engine cold)
Some Dellortos have a cold start circuit (choke), others don't, in my experience, it is very easy to flood the engine and wet plugs using the cold start mechanism, as it very crude in operation. The accepted technique for cold starting is as follows:-
Allow the float chambers to fill if you have an electric pump, this should take about 5-10 seconds, fully depress the accelerator rapidly four times, then on a light throttle, turn the engine over, if it does not start immediately, repeat the procedure three times. The engine should fire, but may need 'nursing' for a minute or two before it will idle, gentle prodding of the accelerator should keep it alive long enough for it to warm up. If the engine does not fire within three attempts, then try five or six pumps. If this does not work, depress the accelerator fully and hold it open while turning the engine over for 5 to 15 seconds, then close the accelerator and try again.
Buying second-hand
When buying Dellortos second-hand ensure that they are a matched pair. Look carefully at the serial numbers on the top of the carbs, these should be the same, or very similar. If they are not then they are not a matched pair and may well give problems when trying to jet them, as the progression drillings could be different. Inspect the carbs very carefully before parting with your cash, check their general condition, check for fire/heat damage, check that the butterflies open and close smoothly and that the linkages are smooth in operation and the carbs don't stick open. A common problem with Dellortos is the attachment of the throttle quadrant to the spindle, these can wear and will give an erratic idle and progression which no amount of tuning will cure. It is important to note that Dellortos are very rarely 'ready jetted' so factor the cost of jets etc. when deciding on your purchase. Check the throttle spindles for wear, excessive wear here will bleed air into the engine and again will affect setting up dramatically. Servicing kits for Dellortos are relatively cheap so a neglected pair, provided that the above checks are carried out, can be restored to very good condition by a thorough clean and service, the servicing is not difficult but has to be done in a clean environment, using a methodical approach.
Credit to Dave Andrews for above info
Last edited by installer67; 04-02-10 at 01:04 PM.
The following users liked this post:
ToughMedic68 (09-16-19)
04-02-10, 01:19 PM
#4
Here's a link to Peejay's post here in the club on his Dellorto. Very informative.
https://www.rx7club.com/1st-generation-specific-1979-1985-18/dellorto-48-dhla-swap-13b-12a-not-56k-friendly-773154/
https://www.rx7club.com/1st-generation-specific-1979-1985-18/dellorto-48-dhla-swap-13b-12a-not-56k-friendly-773154/
04-02-10, 01:34 PM
#7
Gruntled.com
Copied from Gruntled.com
Brad Page’s Experience using a 12A Street-Port
I’ve had a Dellorto 48 DHLA on my streetported 12A since January 1999 and have been tuning it extensively. The jetting that Racing Beat installed on the carb was designed for a stock port 12A motor and is inadequate for a streetported motor. I did find an improvement by going to larger main fuel and smaller main air jets, as well as larger idle fuel jet (this helped the progression stage of the carb a lot). The problem with the Dellorto setup is not the carb, it’s the horrible manifold that Racing Beat designed for it. It’s a 2 piece manifold, the upper piece is the same for 12A and 13B models. The bottom piece must be purchased from RB for the 12A; and the upper piece bolts to the stock intake manifold for the 13B. This was done for ease of install and lower cost for the 13B owners, which in a nutshell resulted in restriction. Read on for details.
Some people say Weber is better than Dellorto, but the Dellorto is a fine carb. At European Motorworks, the local carb shop I go to for my jets and carb parts, I see just as many Dellorto’s as Weber’s. Dellorto took the basic design from Weber and improved upon it and used more modern manufacturing techniques. It has more progression holes, non-brass floats (like Weber), a wider range of jets with more choices within the range, and several small details. The 48mm DHLA can supply my thirsty 12A streetport with pleanty of fuel and make good power.
The jetting that Racing Beat put in their carb, as intended to be installed on a stock port 12A with RB exhaust and RB intake manifold is:
230 main fuel
230 air correction
.8 emulsion tube
75 Idle fuel jet
.4 Idle jet holder (air jet)
39mm chokes
.1 auxiliary venturi
95 starter jet
80 accelerator pump jet
Keep in mind the .8 emulsion tube has had several holes drilled in it by Racing Beat, to facilitate a leaner mixture above idle. There are about 20 holes total in the e-tube. A normal .8 emulstion tube will be too rich. You can still buy the RB .8 e-tube from RB. What I ended up with on my streetported 12A with RB’s intake manifold RB dual presilencer exhaust system and primaflow muffler is:
240 main fuel
210 air correction
.8 emulsion tube
80 Idle fuel jet
.4 Idle jet holder (air jet)
39mm chokes
.1 auxiliary venturi
95 starter jet
80 accelerator pump jet
3 ½ turns out on the idle fuel mixture
The 80 idle fuel jet was too small, which made the motor run real lean on the progression circuit. My A/F meter pegged on the lean end of the meter fora sec or two during hard acceleration; and I tried 85’s which were way too big. I think 82’s are a good compromise. I also tried a 90 accelerator pump jet and it seemed to help a little, but I’m not sold on it.
I noticed the RB manifold, which is U shaped and has 2 sharp bends, is very restrictive. A shop that flows and ports manifolds told me this too :-] It’s throttle response is not all that good, and it’s rather lazy off the line. Also it flows like **** above 7000rpm. At the track I was shifting at 7K. Anything above that and I was just spinning the motor. A streetported rotary has it’s powerband from 5k - 8k. The manifold never let me get into the top of my powerband. This is the reason why Racing Beat couldn’t make a good street port Dellorto setup. NOT the carb. Try blowing air thru a bent straw and you’ll know what I mean. No one can not seriously tell me that Dellorto’s are the hot setup on 914’s, air-cooled VW’s, and Mercury Capri Karmann built 6 cyl, but for some mysterious reason it falls on it’s face when bolted up to a rotary. March 1999 I installed an intake manifold built by Lake Cities Rotary. It’s 4” long, horizontal with NO BENDS, allows the carb to have a straight shot at the intake ports like a true sidedraft should, and is the only manifold positioning the carb beside the motor and not on top. Unfortunately it’s also above the headers which are real hot, but I adapted the stock heat shield to fit over my headers, by building a bracket so it’ll bolt onto the two upper header bolts which cooled down the carb and manifold a bit. Also pointed one of my cold-air induction tubes towards the manifold. All this really reduced under-hood engine temps. Needless to say the manifold flows great, and absolutely positively screams over 6k. MUCH BETTER THAN THE RACING BEAT MANIFOLD. Day and night. I never knew my motor could revv up that quickly. But that was with the 39mm chokes, which were way too big for this manifold and my low end torque sucked (below 5K not much oomph). This manifold was originally designed for a Weber 45 DCOE with 36mm chokes.
I have just started to rejet it with 37mm chokes and this is what I have so far:
190 main fuel
220 air correction
.8 emulsion tube
82 Idle fuel jet
.4 Idle jet holder (air jet)
**** 37mm chokes ****
.1 auxiliary venturi
95 starter jet
80 accelerator pump jet
2 turns out on the idle fuel mixture
Here I am using cheapo 30mm tall velocity stacks and a 90mm tall foam ITG air filter. The stacks inside diameter are a little small and restrictive. I gotta try different air/fuel jets but this is a good start. Much better low end torque than with the 39mm chokes, about what the RB manifold has, and with the LC manifold it revs much better over 6K. Really allows the enlarged engine ports to flow. I think this manifold added at least 5hp. Frey Racing dynoed the manifold as adding 15 more horsepower to a streetported 12A, but I think that’s a little optimistic. BTW the LC manifold is not made anymore thru LC. Atkins Rotary sells it for $200.00 but if you post ads on the internet someone might respond with a used one for less$.
June 2000 I now use the 39mm chokes with the LC manifold since I only use the rx7 on the racetrack now for drivers schools. I am now using TWM induction 50mm tall velocity stacks and a K&N 3 ¼” tall air filter. The air filter barely fits inbetween the carb and thr passenger side frame rail/unibody. Not much torque below 4000rpm. The motor doesn’t wake up till 5000rpm but that’s fine for a track car!!! The carb’s jetted like this:
180 main fuel
210 air correction
.8 emulsion tube
80 Idle fuel jet
.4 Idle jet holder (air jet)
39mm chokes
.1 auxiliary venturi
95 starter jet
90 accelerator pump jet ** seems to like the 90’s.
2 ½ turns out on the idle fuel mixture
January 2001 I just installed some 40mm chokes since the motor didn’t wind out as much as I wanted it to over 8000rpm with the 39’s and that’s a bad thing since my peak horsepower and shift point is at 8500rpm. I will start tuning the carb next month. I’m having a close ratio tranny built to keep the motor in it’s narrow rpm range.If you want to buy different jets, try cbperformance.com or European Motorworks @ 1-800-722-8678. The latter has really helped me out.
Brad Page’s Experience using a 12A Street-Port
I’ve had a Dellorto 48 DHLA on my streetported 12A since January 1999 and have been tuning it extensively. The jetting that Racing Beat installed on the carb was designed for a stock port 12A motor and is inadequate for a streetported motor. I did find an improvement by going to larger main fuel and smaller main air jets, as well as larger idle fuel jet (this helped the progression stage of the carb a lot). The problem with the Dellorto setup is not the carb, it’s the horrible manifold that Racing Beat designed for it. It’s a 2 piece manifold, the upper piece is the same for 12A and 13B models. The bottom piece must be purchased from RB for the 12A; and the upper piece bolts to the stock intake manifold for the 13B. This was done for ease of install and lower cost for the 13B owners, which in a nutshell resulted in restriction. Read on for details.
Some people say Weber is better than Dellorto, but the Dellorto is a fine carb. At European Motorworks, the local carb shop I go to for my jets and carb parts, I see just as many Dellorto’s as Weber’s. Dellorto took the basic design from Weber and improved upon it and used more modern manufacturing techniques. It has more progression holes, non-brass floats (like Weber), a wider range of jets with more choices within the range, and several small details. The 48mm DHLA can supply my thirsty 12A streetport with pleanty of fuel and make good power.
The jetting that Racing Beat put in their carb, as intended to be installed on a stock port 12A with RB exhaust and RB intake manifold is:
230 main fuel
230 air correction
.8 emulsion tube
75 Idle fuel jet
.4 Idle jet holder (air jet)
39mm chokes
.1 auxiliary venturi
95 starter jet
80 accelerator pump jet
Keep in mind the .8 emulsion tube has had several holes drilled in it by Racing Beat, to facilitate a leaner mixture above idle. There are about 20 holes total in the e-tube. A normal .8 emulstion tube will be too rich. You can still buy the RB .8 e-tube from RB. What I ended up with on my streetported 12A with RB’s intake manifold RB dual presilencer exhaust system and primaflow muffler is:
240 main fuel
210 air correction
.8 emulsion tube
80 Idle fuel jet
.4 Idle jet holder (air jet)
39mm chokes
.1 auxiliary venturi
95 starter jet
80 accelerator pump jet
3 ½ turns out on the idle fuel mixture
The 80 idle fuel jet was too small, which made the motor run real lean on the progression circuit. My A/F meter pegged on the lean end of the meter fora sec or two during hard acceleration; and I tried 85’s which were way too big. I think 82’s are a good compromise. I also tried a 90 accelerator pump jet and it seemed to help a little, but I’m not sold on it.
I noticed the RB manifold, which is U shaped and has 2 sharp bends, is very restrictive. A shop that flows and ports manifolds told me this too :-] It’s throttle response is not all that good, and it’s rather lazy off the line. Also it flows like **** above 7000rpm. At the track I was shifting at 7K. Anything above that and I was just spinning the motor. A streetported rotary has it’s powerband from 5k - 8k. The manifold never let me get into the top of my powerband. This is the reason why Racing Beat couldn’t make a good street port Dellorto setup. NOT the carb. Try blowing air thru a bent straw and you’ll know what I mean. No one can not seriously tell me that Dellorto’s are the hot setup on 914’s, air-cooled VW’s, and Mercury Capri Karmann built 6 cyl, but for some mysterious reason it falls on it’s face when bolted up to a rotary. March 1999 I installed an intake manifold built by Lake Cities Rotary. It’s 4” long, horizontal with NO BENDS, allows the carb to have a straight shot at the intake ports like a true sidedraft should, and is the only manifold positioning the carb beside the motor and not on top. Unfortunately it’s also above the headers which are real hot, but I adapted the stock heat shield to fit over my headers, by building a bracket so it’ll bolt onto the two upper header bolts which cooled down the carb and manifold a bit. Also pointed one of my cold-air induction tubes towards the manifold. All this really reduced under-hood engine temps. Needless to say the manifold flows great, and absolutely positively screams over 6k. MUCH BETTER THAN THE RACING BEAT MANIFOLD. Day and night. I never knew my motor could revv up that quickly. But that was with the 39mm chokes, which were way too big for this manifold and my low end torque sucked (below 5K not much oomph). This manifold was originally designed for a Weber 45 DCOE with 36mm chokes.
I have just started to rejet it with 37mm chokes and this is what I have so far:
190 main fuel
220 air correction
.8 emulsion tube
82 Idle fuel jet
.4 Idle jet holder (air jet)
**** 37mm chokes ****
.1 auxiliary venturi
95 starter jet
80 accelerator pump jet
2 turns out on the idle fuel mixture
Here I am using cheapo 30mm tall velocity stacks and a 90mm tall foam ITG air filter. The stacks inside diameter are a little small and restrictive. I gotta try different air/fuel jets but this is a good start. Much better low end torque than with the 39mm chokes, about what the RB manifold has, and with the LC manifold it revs much better over 6K. Really allows the enlarged engine ports to flow. I think this manifold added at least 5hp. Frey Racing dynoed the manifold as adding 15 more horsepower to a streetported 12A, but I think that’s a little optimistic. BTW the LC manifold is not made anymore thru LC. Atkins Rotary sells it for $200.00 but if you post ads on the internet someone might respond with a used one for less$.
June 2000 I now use the 39mm chokes with the LC manifold since I only use the rx7 on the racetrack now for drivers schools. I am now using TWM induction 50mm tall velocity stacks and a K&N 3 ¼” tall air filter. The air filter barely fits inbetween the carb and thr passenger side frame rail/unibody. Not much torque below 4000rpm. The motor doesn’t wake up till 5000rpm but that’s fine for a track car!!! The carb’s jetted like this:
180 main fuel
210 air correction
.8 emulsion tube
80 Idle fuel jet
.4 Idle jet holder (air jet)
39mm chokes
.1 auxiliary venturi
95 starter jet
90 accelerator pump jet ** seems to like the 90’s.
2 ½ turns out on the idle fuel mixture
January 2001 I just installed some 40mm chokes since the motor didn’t wind out as much as I wanted it to over 8000rpm with the 39’s and that’s a bad thing since my peak horsepower and shift point is at 8500rpm. I will start tuning the carb next month. I’m having a close ratio tranny built to keep the motor in it’s narrow rpm range.If you want to buy different jets, try cbperformance.com or European Motorworks @ 1-800-722-8678. The latter has really helped me out.
Trending Topics
04-02-10, 01:45 PM
#8
List of parts and part #s for attache diagram DHLA
Diag # Diag Part # Description Sizes/options available
1 8564 DHLA 48 choke 41,42,43mm 48 7540 O ring
2 7956 DHLA 45/48 choke 31,32,33,34,35,36,37,38,39,40mm 49 7513 Cap screw Carb details required.
2 8383 DHLA 40 choke 25 to 37mm, in 1mm steps 50 7525 Pump jet weight Carb details required.
3 8011 DHLA 45/48 Aux. Venturi 1,2,3,4 51 6415 Pump jet ball bearing
4 7848 DHLA 40 Aux. Venturi 1,2,3,4 52 10747 Pump jet holder
5 7484 Main Jet 85,88,90,92,95,98,100 etc to 110, 53 10748 Pump jet filter/spring
5 110-190 in 1`s 202,205,208,210-240, in 5`s 54 6173 Pump jet O ring
6 7644 Idle jet 32-82 in 1`s 55 6426 Pump jet cap fibre washer
7 7851 Pump jet 30,33,35,38,40,42,45,48,55,60,65, 56 9926 Air bleed screw Carb details required.
7 70,75,90,150. 57 8678 Air bleed screw O ring
8 3315 Starter jet 40-90 in 5`s 58 7959 Vacuum blanking screw
9 7772 Main emulsion tube No`s 1 to 16 59 8857 G/H prog. blanking screw Carb details required.
10 7482 Starter emulsion tube No`s 1,2,3,4 60 9656 Mixture screw 48/45/40H Carb details required.
11 7485 Air corrector 80,90,100,110,115,120,125,130,135 61 9336 Mixture screw spring
11 140,142.5-202.5 in 2.5`s 205-250. 62 8260 Mixture screw washer
12 7850 Idle holder/emulsion tube Weak- 5,10,9,4,1,3,6,7,2,8 -rich 63 10381 DHLA late alfa lever
13 8809 Needle valve, viton tipped 120,150,170,200,225 64 9754 DHLA throttle stop screw
13 8811 Needle valve, metal tipped 120, 150, 170, 200, 225. 65 6423 Spindle nut (also locking washer on 91) 12538 Needle valve, viton tipped 350 (cross drilled) 66 6581 Spindle nut lock washer
14 7481 Throttle butterfly DHLA 40 Carb details required. 67 10714 Short Lotus lever
14 8010 Throttle butterfly DHLA 45 Carb details required. 68 7958 Spindle end cover
14 8563 Throttle butterfly DHLA 48 Carb details required. 69 7537 Spindle washer
15 7298 Float assy 70 7490 Spindle bearing
16 7501 Choke piston cover bolt Carburettor reconditioning 71 7627 Pump rod spring Carb details required.
17 7413 Choke piston spring service available. 72 8058 40/45/48 E Pump Cover assy Carb details required.
18 9609 Choke piston 73 7625 Pump rod nut
19 6434 Choke outer cable clamp screw 74 6390 Pump rod lock nut
20 7488 Choke cable support 75 7626 Diaphagm Spring
21 9818 Top cover casting Carb details required. 76 7515 Pump Diaphragm Carb details required.
22 9358 Top cover casting gasket 77 5011 Spring washer (pump cover)
22 9220 Top cover casting gasket (antisurge) 78 6429 Screw (pump cover)
23 9498 Needle valve filter 79 8302 Alfa carb/inlet manifold gasket Carb details required.
24 7530 Vent cover screw 80 7542 Pump non-return valve
25 7549 Vent cover (plastic) (alloy available) 81 7509 Pump body gasket
26 6430 Top cover screw 82 7550 DHLA45E Pump body Carb details required.
27 4997 Top cover spring washer 83 7526 Pump body screw
28 7511 Vent cover gasket All parts for Lotus & turbo 84 6416 Butterfly screw
29 7062 Choke inner cable clamp DHLA`S available 85 6449 DHLA48 choke retaining screw Required on 48`s only
30 6850 Cable clamp washer 86 4957 Spring washer (choke screw)
31 6432 Choke cable clamp nut 87 7151 Trumpet stud Carb details required.
32 7854 Choke cable return spring 88 7957 Throttle return spring (std)
33 7838 Choke spring cup washer 88 8610 Throttle return spring (competition)
34 4957 Spring washer 89.9024 6887.596341 Cap screw Carb details required.
35 2906 Choke spring retaining nut 90 8307 DHLA40 pump rod assy
36 9610 Choke actuator cam 91 7507 Venturi grub screw
37 7837 Actuator cam spring washer 92 3793 Split pin (balance lever) Carburettor reconditioning
38 9611 Actuator cam retaining bush Carb details required. 93 7496 Balance lever pin service available.
39 7341 Choke actuator lever 93 9752 Balance lever pin
40 6425 Needle valve washer 94 2638 Balance lever spring
41 7503 Float assy pivot pin 95 11529 Late Alfa balance lever
42 7663 Banjo fibre washer, inner 96 7496 Balance lever pin
43 7862 Fuel banjo, single 45 degree 97 6898 Throttle stop screw
43 8071 Fuel banjo, single 90 degree Carburettor reconditioning 98 4670 Throttle stop screw spring
43 7660 Fuel banjo, single standard service available. 99 4650 Washer
44 8072 Fuel banjo, double 90 degree 100 8304 Lotus balance lever All parts for Lotus & turbo
44 7661 Fuel banjo, double standard 101 7668 DHLA 40 spindle DHLA`S available
45 1419 Banjo fuel filter 101 8352 DHLA 45 spindle
46 7662 Banjo fibre washer, outer 101 8604 DHLA 48 spindle
47 7659 Banjo bolt 102 52528 Gasket set (2 carbs)
1 8564 DHLA 48 choke 41,42,43mm 48 7540 O ring
2 7956 DHLA 45/48 choke 31,32,33,34,35,36,37,38,39,40mm 49 7513 Cap screw Carb details required.
2 8383 DHLA 40 choke 25 to 37mm, in 1mm steps 50 7525 Pump jet weight Carb details required.
3 8011 DHLA 45/48 Aux. Venturi 1,2,3,4 51 6415 Pump jet ball bearing
4 7848 DHLA 40 Aux. Venturi 1,2,3,4 52 10747 Pump jet holder
5 7484 Main Jet 85,88,90,92,95,98,100 etc to 110, 53 10748 Pump jet filter/spring
5 110-190 in 1`s 202,205,208,210-240, in 5`s 54 6173 Pump jet O ring
6 7644 Idle jet 32-82 in 1`s 55 6426 Pump jet cap fibre washer
7 7851 Pump jet 30,33,35,38,40,42,45,48,55,60,65, 56 9926 Air bleed screw Carb details required.
7 70,75,90,150. 57 8678 Air bleed screw O ring
8 3315 Starter jet 40-90 in 5`s 58 7959 Vacuum blanking screw
9 7772 Main emulsion tube No`s 1 to 16 59 8857 G/H prog. blanking screw Carb details required.
10 7482 Starter emulsion tube No`s 1,2,3,4 60 9656 Mixture screw 48/45/40H Carb details required.
11 7485 Air corrector 80,90,100,110,115,120,125,130,135 61 9336 Mixture screw spring
11 140,142.5-202.5 in 2.5`s 205-250. 62 8260 Mixture screw washer
12 7850 Idle holder/emulsion tube Weak- 5,10,9,4,1,3,6,7,2,8 -rich 63 10381 DHLA late alfa lever
13 8809 Needle valve, viton tipped 120,150,170,200,225 64 9754 DHLA throttle stop screw
13 8811 Needle valve, metal tipped 120, 150, 170, 200, 225. 65 6423 Spindle nut (also locking washer on 91) 12538 Needle valve, viton tipped 350 (cross drilled) 66 6581 Spindle nut lock washer
14 7481 Throttle butterfly DHLA 40 Carb details required. 67 10714 Short Lotus lever
14 8010 Throttle butterfly DHLA 45 Carb details required. 68 7958 Spindle end cover
14 8563 Throttle butterfly DHLA 48 Carb details required. 69 7537 Spindle washer
15 7298 Float assy 70 7490 Spindle bearing
16 7501 Choke piston cover bolt Carburettor reconditioning 71 7627 Pump rod spring Carb details required.
17 7413 Choke piston spring service available. 72 8058 40/45/48 E Pump Cover assy Carb details required.
18 9609 Choke piston 73 7625 Pump rod nut
19 6434 Choke outer cable clamp screw 74 6390 Pump rod lock nut
20 7488 Choke cable support 75 7626 Diaphagm Spring
21 9818 Top cover casting Carb details required. 76 7515 Pump Diaphragm Carb details required.
22 9358 Top cover casting gasket 77 5011 Spring washer (pump cover)
22 9220 Top cover casting gasket (antisurge) 78 6429 Screw (pump cover)
23 9498 Needle valve filter 79 8302 Alfa carb/inlet manifold gasket Carb details required.
24 7530 Vent cover screw 80 7542 Pump non-return valve
25 7549 Vent cover (plastic) (alloy available) 81 7509 Pump body gasket
26 6430 Top cover screw 82 7550 DHLA45E Pump body Carb details required.
27 4997 Top cover spring washer 83 7526 Pump body screw
28 7511 Vent cover gasket All parts for Lotus & turbo 84 6416 Butterfly screw
29 7062 Choke inner cable clamp DHLA`S available 85 6449 DHLA48 choke retaining screw Required on 48`s only
30 6850 Cable clamp washer 86 4957 Spring washer (choke screw)
31 6432 Choke cable clamp nut 87 7151 Trumpet stud Carb details required.
32 7854 Choke cable return spring 88 7957 Throttle return spring (std)
33 7838 Choke spring cup washer 88 8610 Throttle return spring (competition)
34 4957 Spring washer 89.9024 6887.596341 Cap screw Carb details required.
35 2906 Choke spring retaining nut 90 8307 DHLA40 pump rod assy
36 9610 Choke actuator cam 91 7507 Venturi grub screw
37 7837 Actuator cam spring washer 92 3793 Split pin (balance lever) Carburettor reconditioning
38 9611 Actuator cam retaining bush Carb details required. 93 7496 Balance lever pin service available.
39 7341 Choke actuator lever 93 9752 Balance lever pin
40 6425 Needle valve washer 94 2638 Balance lever spring
41 7503 Float assy pivot pin 95 11529 Late Alfa balance lever
42 7663 Banjo fibre washer, inner 96 7496 Balance lever pin
43 7862 Fuel banjo, single 45 degree 97 6898 Throttle stop screw
43 8071 Fuel banjo, single 90 degree Carburettor reconditioning 98 4670 Throttle stop screw spring
43 7660 Fuel banjo, single standard service available. 99 4650 Washer
44 8072 Fuel banjo, double 90 degree 100 8304 Lotus balance lever All parts for Lotus & turbo
44 7661 Fuel banjo, double standard 101 7668 DHLA 40 spindle DHLA`S available
45 1419 Banjo fuel filter 101 8352 DHLA 45 spindle
46 7662 Banjo fibre washer, outer 101 8604 DHLA 48 spindle
47 7659 Banjo bolt 102 52528 Gasket set (2 carbs)
04-02-10, 01:48 PM
#9
Jetting
Jetting (also copied from Gruntled.com)
There is no one correct set of jets to use, however there are some good ballpark settings for each application (i.e. 12A stock, street-port, etc.). Racing Beat delivered a carburetor that was set up to provide good performance out of the box with only minor tweaking of the idle mixture screw. Of course even that setup is probably not optimum for all applications as other engine modifications and elevation play a role. However, the average person doesn’t have the time, equipment, and knowledge to find the optimum set-up. My goal with this page is to provide the set-up that Racing Beat delivered (it works for most) and also information from other people on their individual set-ups.
This section is not as complete as it could be as I don’t even have the exact settings that Racing Beat used. Also it is quite possible that Racing Beat changed their jetting settings over time. Also Racing Beat modified the carburetor as delivered by Dellorto. I am not sure what exact changes they made.
12A Engines
12A Stock (from RB)
These settings are from my carburetor. In a few cases I am not 100% sure of the jet size and I won’t tear my carburetor apart just to find out. After my last experience with the pump jet, I need a good reason to tear into it again.
Jet
Size
Notes
Main Emulsion Tube
#7772.8
Main Fuel Jet
#230
Main Air Jet
#230
Idle Holder/Emulsion Tube
#7850.4
Idle Jet
#75
Accelerator Pump Jet
#90
Not positive on this.
Needle and Seat
#300
Pretty sure as it’s the only one that RB had in their catalog.
12A Stock (from Will Claypole) New!
This page is a write-up by Will on his experience getting the Dellorto working on a stock 12A. Will did considerable tinkering with the carburetor to improve the original RB setup. Major changes include modifying the float level and the accelerator pump.
12A Street-Port (from Brad Page)
This page is a write-up by Brad on his experience getting the Dellorto to work well with his street-ported 12A. He found that the intake manifold by Racing Beat to be the reason why people (including RB) have problems getting the Dellorto to work well with a ported engine.
13B Engines
6-Port 13B Stock (from RB) New!
I received settings from Daniel Ciarcia who got them from Racing Beat. Mazdatrix and Hayes also recommended these settings. Only the accelerator pump jet and emulsion tube are different from the 12A setup.
Jet
Size
Notes
Main Emulsion Tube
#7772.8
Main Fuel Jet
#230
Main Air Jet
#230
Idle Holder/Emulsion Tube
#7850.8
Idle Jet
#75
Accelerator Pump Jet
#80
Needle and Seat
#300
6-Port Street-Port 13B
If anyone has settings for this setup please let me know (dave@gruntled.com).
There is no one correct set of jets to use, however there are some good ballpark settings for each application (i.e. 12A stock, street-port, etc.). Racing Beat delivered a carburetor that was set up to provide good performance out of the box with only minor tweaking of the idle mixture screw. Of course even that setup is probably not optimum for all applications as other engine modifications and elevation play a role. However, the average person doesn’t have the time, equipment, and knowledge to find the optimum set-up. My goal with this page is to provide the set-up that Racing Beat delivered (it works for most) and also information from other people on their individual set-ups.
This section is not as complete as it could be as I don’t even have the exact settings that Racing Beat used. Also it is quite possible that Racing Beat changed their jetting settings over time. Also Racing Beat modified the carburetor as delivered by Dellorto. I am not sure what exact changes they made.
12A Engines
12A Stock (from RB)
These settings are from my carburetor. In a few cases I am not 100% sure of the jet size and I won’t tear my carburetor apart just to find out. After my last experience with the pump jet, I need a good reason to tear into it again.
Jet
Size
Notes
Main Emulsion Tube
#7772.8
Main Fuel Jet
#230
Main Air Jet
#230
Idle Holder/Emulsion Tube
#7850.4
Idle Jet
#75
Accelerator Pump Jet
#90
Not positive on this.
Needle and Seat
#300
Pretty sure as it’s the only one that RB had in their catalog.
12A Stock (from Will Claypole) New!
This page is a write-up by Will on his experience getting the Dellorto working on a stock 12A. Will did considerable tinkering with the carburetor to improve the original RB setup. Major changes include modifying the float level and the accelerator pump.
12A Street-Port (from Brad Page)
This page is a write-up by Brad on his experience getting the Dellorto to work well with his street-ported 12A. He found that the intake manifold by Racing Beat to be the reason why people (including RB) have problems getting the Dellorto to work well with a ported engine.
13B Engines
6-Port 13B Stock (from RB) New!
I received settings from Daniel Ciarcia who got them from Racing Beat. Mazdatrix and Hayes also recommended these settings. Only the accelerator pump jet and emulsion tube are different from the 12A setup.
Jet
Size
Notes
Main Emulsion Tube
#7772.8
Main Fuel Jet
#230
Main Air Jet
#230
Idle Holder/Emulsion Tube
#7850.8
Idle Jet
#75
Accelerator Pump Jet
#80
Needle and Seat
#300
6-Port Street-Port 13B
If anyone has settings for this setup please let me know (dave@gruntled.com).
04-02-10, 01:52 PM
#10
Accelerator Pump Jet (Gruntled.com)
Here's a case of "if it ain't broke, don't fix it". I had my Dellorto system on the shelf for about 6 years due to emissions regulations. I then decided to put it back on since the car is no longer a daily driver and I wanted to race it in Autocross. The carburetor was very clean because I had stored it in a plastic bag to keep the dust and grunge out. Being curious I started to inspect the carburetor by removing some of the jets to look for varnish an any other signs of wear. Everything was spotless so I put it on the car.
After completing the installation, the car started right up. So far so good. However, if I quickly (or normally) depressed the accelerator, the car would choke and die. This happened every time. If I very slowly depressed the accelerator, the engine would gradually increase in RPM all the way to red-line. I figured that it wasn't getting enough gas when pressing the gas pedal. Sure enough, that's what was happening. Here's were our friend the Pump Jet comes in.
The Pump Jet meters the flow of fuel from the accelerator pump directly into the throttle bores. I needed to see if gas was squirting when the throttle moved without having to remove the carburetor. I removed one of the Pump Jets and hit the throttle. Sure enough gas shot out of the little hole and down into the bore.
I started inspecting the Pump Jet to see if there was some kind of blockage. There wasn't any. The Pump Jet has a flat spot that matches with flat area in the carburetor body, so it can only go in one way. In the photograph above, you can see a slot in the Pump Jet. When inserted into the body, that slot lines up with the fuel supply hole (for lack of a better term). Now look at the Jet Holder. The Holder screws into the body and is what holds the Pump Jet in place. Notice that there is a hole in the Holder. Since the Jet sits inside of the Holder, the hole in the Holder MUST line up EXACTLY with the hole in the body! When lined up, fuel flows out the hole in the body, through the hole in the Holder, then through the slot in the Jet, and finally down the Jet and into the throttle bore.
If the O-ring and/or washer are compressed or deformed (this happens over time), then the Jet Holder must be turned further, in order to get it tight enough to hold everything in place. If that happens then the hole won't line up and fuel flow will be BLOCKED! This is why the engine was dying when I hit the accelerator. The throttle opened up which allowed a large amount of air to flow into the engine but there was no fuel coming out of the Pump Jets. This caused an extremely lean condition which killed the motor.
To fix this, I had to locate a rebuild kit to get new O-rings and washers. I purchased a rebuild kit from CB Performance and the O-ring was slightly fuller than the old one, but the new washer was actually thinner than the original. I was expecting a bigger washer. In any case, I ended up stacking both washers together and using the new O-rings to get the holes to align, while under sufficient torque to hold everything in place.
There's one other tip. The Holders have vertical marks on them which I assume are supposed to mark the location of the hole. One of mine did not line up so I had to use a Sharpie to mark the location. I then carefully tightened the Holder until the marks lined up with a ridge on the body that has the fuel passageway.
This is definitely one part that you should not remove or loosen unless you have to, and you have new parts for a rebuild.
Here's a case of "if it ain't broke, don't fix it". I had my Dellorto system on the shelf for about 6 years due to emissions regulations. I then decided to put it back on since the car is no longer a daily driver and I wanted to race it in Autocross. The carburetor was very clean because I had stored it in a plastic bag to keep the dust and grunge out. Being curious I started to inspect the carburetor by removing some of the jets to look for varnish an any other signs of wear. Everything was spotless so I put it on the car.
After completing the installation, the car started right up. So far so good. However, if I quickly (or normally) depressed the accelerator, the car would choke and die. This happened every time. If I very slowly depressed the accelerator, the engine would gradually increase in RPM all the way to red-line. I figured that it wasn't getting enough gas when pressing the gas pedal. Sure enough, that's what was happening. Here's were our friend the Pump Jet comes in.
The Pump Jet meters the flow of fuel from the accelerator pump directly into the throttle bores. I needed to see if gas was squirting when the throttle moved without having to remove the carburetor. I removed one of the Pump Jets and hit the throttle. Sure enough gas shot out of the little hole and down into the bore.
I started inspecting the Pump Jet to see if there was some kind of blockage. There wasn't any. The Pump Jet has a flat spot that matches with flat area in the carburetor body, so it can only go in one way. In the photograph above, you can see a slot in the Pump Jet. When inserted into the body, that slot lines up with the fuel supply hole (for lack of a better term). Now look at the Jet Holder. The Holder screws into the body and is what holds the Pump Jet in place. Notice that there is a hole in the Holder. Since the Jet sits inside of the Holder, the hole in the Holder MUST line up EXACTLY with the hole in the body! When lined up, fuel flows out the hole in the body, through the hole in the Holder, then through the slot in the Jet, and finally down the Jet and into the throttle bore.
If the O-ring and/or washer are compressed or deformed (this happens over time), then the Jet Holder must be turned further, in order to get it tight enough to hold everything in place. If that happens then the hole won't line up and fuel flow will be BLOCKED! This is why the engine was dying when I hit the accelerator. The throttle opened up which allowed a large amount of air to flow into the engine but there was no fuel coming out of the Pump Jets. This caused an extremely lean condition which killed the motor.
To fix this, I had to locate a rebuild kit to get new O-rings and washers. I purchased a rebuild kit from CB Performance and the O-ring was slightly fuller than the old one, but the new washer was actually thinner than the original. I was expecting a bigger washer. In any case, I ended up stacking both washers together and using the new O-rings to get the holes to align, while under sufficient torque to hold everything in place.
There's one other tip. The Holders have vertical marks on them which I assume are supposed to mark the location of the hole. One of mine did not line up so I had to use a Sharpie to mark the location. I then carefully tightened the Holder until the marks lined up with a ridge on the body that has the fuel passageway.
This is definitely one part that you should not remove or loosen unless you have to, and you have new parts for a rebuild.
04-03-10, 02:37 AM
#16
Jolly Green Giant
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Join Date: Feb 2008
Location: San Antonio, TX
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Installer....I Think I love you....finally a ton of Dellorto stuff in one place. AWESOME!!!!!!! seen some stuff I've got and some stuff I haven't like the float stuff which I have been looking for since the beginning of time.
ARCHIVE!
ARCHIVE!
04-03-10, 07:23 AM
#23
DHLA type/models explained
Type 1 the first DHLA40 (no letter after) if you like the DCOE of the DHLA family, but boasts superior atomisation and tuning ability to the extra research at Dellorto…This carb has an idle jet (which also runs the progression and adds mixture at cruising) that is not connected to the main jet stack, the idle jet operates on its own from the float bowl. Also the idle jet air feed for the emulsion tube is ot fixed at a set size like later models…The main jets run on their own from the float bowl like the idle’s…This gives two seperate circuits that must be tuned for perfect overlap to get good cruise and pickup….This has the benefit on small engines and racing engines and hard tuned engines of giving the ability to make the idle jet progress long or short, you can bring the mains in early and cut back the progression on the idle jet air feed with differing jet holders with differing sized air holes, more air, bigger hole less progression….So you can tune this carb a million ways for million application, Fewsters just got a pair of these. They are the ulimate in tuneablity, they are also as a downside extremely hard to tune without a massive jet box or rolling road, cause they need to be bang on the money. This type of carb uses a .1 venturi which has a bigger pilot hole that the .2 and .3 (ill cover later), this means a bigger signal is generated in the venturi tube which gives a bigger signal (pulsing) to the main jet stack - the venturi feeds the main power circuit into the engine, the big jets. So the .1 vent can tuned to get on the mains right away from very low rpm and are super responsive to tuning, you can delay the vent by adjusting the tubes and air correctors on the main jet stack, so it needs more signal to start the stack feeding the vent or less setup the opposite way, so they can be tuned many ways also.
Type 2 DHLA40E - These are the same as the DHLA40 with seperate circuits and use either 1 or 2 venturi, they have extra progression holes for the idle jet, so the progression phase can be increased in length (over more plate angle) to suit production cars, and aid economy, real smooth runners when setup with lengthy progression. The 2 vent is just like a 1 with tiny bit smaller bore size to the signal tube, so they have fitted .2 often in the E model as they have extended the progression phase and using the .2 vent means they don’t have to delay the mains as much as fitting the .1 vent, so making jetting easier and more responsive. The Elan +2 used these with the 1 vent as its punchy sports car, the Alfa’s used 2 vent and fitted the E model to flagship models with lazyier owners, who like crisp but relaxed power delivery. Power is equal on both types and they can both delivery the same results.
Type 3 DHLA40F-G-H-N-R-S models. These are called emission completely different to the DCOE science, but noone really understands them and tries always to tune them like the early models. These differ because they have more progression holes and use the idle jet to feed most of the cruise phase and low rpm/low TP area of the engine AT ALL TIMES when the main jet isn’t in operation completely automatically no jetting needed. The idle jet has a very large fixed 2.2mm air feed, you cannot tune this phase of the carburetor for length like the others, but here lays the secrets….
The idle jet doesn’t feed from the float bowl, it feeds directly from the main jet stack, what happens after this is what gives these Dell’Ortos the sweetest road behaviour (what 25years of research came up with and not just for emissions) and dead easy tuning, you see when the main jet starts to emulsify fuel in the tube, the idle jet is feeding from it, so the gassy airy fuel shuts down the idle jet and sucks backwards yes BACKWARDS through the idle!! using every drip of fuel efficiently without ANY waste in circuit cross over where one is going after the other…this happens the moment the main jet fires, so there is NO need at all to tune the length of the progression and idle phase. This is pure magic they are automatically calibrated, you simply keep the idle jet above 59 up to 62 and not make the mistake of fitting numbers suited to the early DHLA or DCOE - with this simple technique you can tune anything from a 1300 to a 2000cc without really doing anything. The emulsion tubes in these carbs are always 8-10-11 and have to stay that way - which are really rich and have a hole straight down with loads of air holes, these atomise the fuel to an massive degree, also they have to be used cause the idle jet will not run correctly using the DHLA40-E type tubes (1-6-7-5) as the idle jet needs these airy tubes to function and cut out as designed…Usually people ram the DHLA40 idle holders with air holes in these carbs add the 1-6-5-7 style tubes and wonder why its a massive lean spot off idle, cause they missed the point completely!…These carbs use a .3 vent which has a very small signal tube to the main jet stack, this is because the holey tubes are basically ready to go from about 1250rpm (on my car using an 8tube 1 vent it was on the mains at 1250rpm!) so the holey tubes need holding back with a signal killing venturi…These carbs are wicked if you want bolt on power, they tune themselves!
The early types are better in respect of punch and tuneability on odd applications but dont’ really do anything these late types won’t on all but the best engines…I have run em all! These carbs will give the maximum power available on any engine if you take time to tune them right, but they are a bit more suited to standard motors over 1500cc, motors with mild cams or standard cams and they operate best if you are using 30-33 chokes, they hate race engines, mad cams and mad chokes cause they they are designed mainly for hot production engines with a clear pulse strength to suit the retarded venturi and tubes - great where silk town driving and alike is paramount and you do commuting or just sunday driving, they also give superior economy to the early types.
So the DCOE is the same as the DHLA40, but the DHLA40E and F-G-H-N-L-R-S are all evolutions of a principle and provided the application is matched to the carbs best qualities you have the ability to cater for everyones tastes and requirements using Dellorto…
Type 2 DHLA40E - These are the same as the DHLA40 with seperate circuits and use either 1 or 2 venturi, they have extra progression holes for the idle jet, so the progression phase can be increased in length (over more plate angle) to suit production cars, and aid economy, real smooth runners when setup with lengthy progression. The 2 vent is just like a 1 with tiny bit smaller bore size to the signal tube, so they have fitted .2 often in the E model as they have extended the progression phase and using the .2 vent means they don’t have to delay the mains as much as fitting the .1 vent, so making jetting easier and more responsive. The Elan +2 used these with the 1 vent as its punchy sports car, the Alfa’s used 2 vent and fitted the E model to flagship models with lazyier owners, who like crisp but relaxed power delivery. Power is equal on both types and they can both delivery the same results.
Type 3 DHLA40F-G-H-N-R-S models. These are called emission completely different to the DCOE science, but noone really understands them and tries always to tune them like the early models. These differ because they have more progression holes and use the idle jet to feed most of the cruise phase and low rpm/low TP area of the engine AT ALL TIMES when the main jet isn’t in operation completely automatically no jetting needed. The idle jet has a very large fixed 2.2mm air feed, you cannot tune this phase of the carburetor for length like the others, but here lays the secrets….
The idle jet doesn’t feed from the float bowl, it feeds directly from the main jet stack, what happens after this is what gives these Dell’Ortos the sweetest road behaviour (what 25years of research came up with and not just for emissions) and dead easy tuning, you see when the main jet starts to emulsify fuel in the tube, the idle jet is feeding from it, so the gassy airy fuel shuts down the idle jet and sucks backwards yes BACKWARDS through the idle!! using every drip of fuel efficiently without ANY waste in circuit cross over where one is going after the other…this happens the moment the main jet fires, so there is NO need at all to tune the length of the progression and idle phase. This is pure magic they are automatically calibrated, you simply keep the idle jet above 59 up to 62 and not make the mistake of fitting numbers suited to the early DHLA or DCOE - with this simple technique you can tune anything from a 1300 to a 2000cc without really doing anything. The emulsion tubes in these carbs are always 8-10-11 and have to stay that way - which are really rich and have a hole straight down with loads of air holes, these atomise the fuel to an massive degree, also they have to be used cause the idle jet will not run correctly using the DHLA40-E type tubes (1-6-7-5) as the idle jet needs these airy tubes to function and cut out as designed…Usually people ram the DHLA40 idle holders with air holes in these carbs add the 1-6-5-7 style tubes and wonder why its a massive lean spot off idle, cause they missed the point completely!…These carbs use a .3 vent which has a very small signal tube to the main jet stack, this is because the holey tubes are basically ready to go from about 1250rpm (on my car using an 8tube 1 vent it was on the mains at 1250rpm!) so the holey tubes need holding back with a signal killing venturi…These carbs are wicked if you want bolt on power, they tune themselves!
The early types are better in respect of punch and tuneability on odd applications but dont’ really do anything these late types won’t on all but the best engines…I have run em all! These carbs will give the maximum power available on any engine if you take time to tune them right, but they are a bit more suited to standard motors over 1500cc, motors with mild cams or standard cams and they operate best if you are using 30-33 chokes, they hate race engines, mad cams and mad chokes cause they they are designed mainly for hot production engines with a clear pulse strength to suit the retarded venturi and tubes - great where silk town driving and alike is paramount and you do commuting or just sunday driving, they also give superior economy to the early types.
So the DCOE is the same as the DHLA40, but the DHLA40E and F-G-H-N-L-R-S are all evolutions of a principle and provided the application is matched to the carbs best qualities you have the ability to cater for everyones tastes and requirements using Dellorto…
04-03-10, 07:57 AM
#24
How to set Floats
This is a great "How To" I found at the Sideways Technologies Forum
How to :
Setup and adjust correct and accurate DHLA40, DHLA45, DHLA48 C,D,E,F,G,H,L,M,P,R,S,T emission and non emission fuel levels and float levels.
First we need to understand there are 3 types of float.
(see float1)
They all look similar! They all need to be catered for in their own setting.
Below shows the EARLY 10gram float, used in some, early types of DHLA40, DHLA40E, DHLA40F (early), also some early DHLA45 and DHLA48
(see float2)
Below shows the 7 and 8.5gram floats which became the "norm" for all carbs after about 1972.
These 7 and 8.5gram are similar in setting, but the 10gram needs a different setting.
(see float3)
I prefer the heavy EARLY 10gram float for some reason, more constant fuel level and running in my opinion. I always fit these to my carbs set at 17.5mm initial setting or 18mm using SUPERIOR Viton Tipped needle valves.
For a given fluid level, a lighter float will naturally ride higher .....
Either the weight or the float part number should be engraved on the float. 3 types the 7g, 8.5g and 10.0g floats.
The basic part number for the floats is 7298-_ _ with two final digits for each specific weight:
01 = 10g 16.5 - 17.0 mm (float height start setting)
02 = 8.5g 15.5 - 16.0 mm
03 = 7.0g 14.5 - 15.0 mm
(see valve1)
Above and below images show the needle valve has a spring inside. ALL static adjustments to float heights MUST be done with the lever tab on the float touching the rounded tip on the needle valve shaft, but NOT compressing the spring at all when the measurement is taken.
(see valve2)
How to :
Setup and adjust correct and accurate DHLA40, DHLA45, DHLA48 C,D,E,F,G,H,L,M,P,R,S,T emission and non emission fuel levels and float levels.
First we need to understand there are 3 types of float.
(see float1)
They all look similar! They all need to be catered for in their own setting.
Below shows the EARLY 10gram float, used in some, early types of DHLA40, DHLA40E, DHLA40F (early), also some early DHLA45 and DHLA48
(see float2)
Below shows the 7 and 8.5gram floats which became the "norm" for all carbs after about 1972.
These 7 and 8.5gram are similar in setting, but the 10gram needs a different setting.
(see float3)
I prefer the heavy EARLY 10gram float for some reason, more constant fuel level and running in my opinion. I always fit these to my carbs set at 17.5mm initial setting or 18mm using SUPERIOR Viton Tipped needle valves.
For a given fluid level, a lighter float will naturally ride higher .....
Either the weight or the float part number should be engraved on the float. 3 types the 7g, 8.5g and 10.0g floats.
The basic part number for the floats is 7298-_ _ with two final digits for each specific weight:
01 = 10g 16.5 - 17.0 mm (float height start setting)
02 = 8.5g 15.5 - 16.0 mm
03 = 7.0g 14.5 - 15.0 mm
(see valve1)
Above and below images show the needle valve has a spring inside. ALL static adjustments to float heights MUST be done with the lever tab on the float touching the rounded tip on the needle valve shaft, but NOT compressing the spring at all when the measurement is taken.
(see valve2)
04-03-10, 08:09 AM
#25
continued .....
Below shows the distance A, which depending on the float used 7,8.5 or 10gram and will be initially set to the figures quoted above. Fit the new valves and assemble the float and cover (with gasket!).
Set your calipers to the figure quote and to work with your float weight, check they are accurate with a ruler or micrometer and proceed to tweak the float, if needed, this is to obtain the correct figure at the floats furthest extremity (A) from the needle valve.
As shown below in other images, to adjust the float level tweak the floats.
(see dhlafloatlevel)
As seen below. It helps to hold the carb top vertically or just off vertical unless you are an octopus. This is so the float tab rests naturally against the needle valves rounded tip.
This MUST be done with the top plate gasket in place.
(see floatinitial)
Most people just finish here and call that setup. This is just stupid, as it often does not translate into a good fuel level in the carb. Depending on if metal or viton tipped needle valved are used and also the valve body can be No1 or No2, floats may have been "butchered" by previous "engineers".
So this is where my technique starts. I use the above info ONLY for reference and initial setup to start off the correct adjustment.
After the above is done, if the carburettors are not bolted to the car, fit them now, but do not fit the top linkage or filters, as you will be removing the float covers and floats and will need to look down the barrels for leaking.
Before adding the fuel pipes to the carbs test the fuel pressure first.
Set at 3psi if using metal valves and up to 5psi if using viton.
Once this is set, fix the fuel pipes to the carbs but do not fill the bowls or operate the electric pump yet. (I hope you are using one!)
Its important to do this on the car, as different fitments/manifolds give a different "angle" or rake to the carb, the main-jet stack must be supplied with a proper fuel level.
Firstly remove two of the top plate cover screws, so each top plate (float cover) is being held down with only two screws.
Below image shows why is it important to leave two screws in place till you are "perfected" in your technique here...
The choke plunger will spring the top plate upwards with no screws in place, so giving a poor reading and leakage if you allow this to happen at any time during this calibration.
Its VERY important to keep the float cover sat firmly on the carb at all times when setting the "fuel bowl levels" ~ to the all important setting so often ignored through ignorance or naivity.
(see top1)
Below shows where the top needs to be while the pump is filling, down on the mating surface, also it needs to be here all the time, till you quickly WHIP it off to check the fuel level.
(see top2)
The gasket needs to be under compression too.
(see caliper27mm)
Get your caliper and set to 27mm!!!!!!!! check the pointy end you will be using is actually set to 27mm in length with a ruler or micrometer and that its accurate to 0.5mm.
You are now ready to fill the fuel bowls. So flick on the pump...Wait for 20seconds. Flick it off, look down inside the barrel into the venturi, if you can see fuel dripping from the venturi the bowl has a bit too much fuel in or you valve is worn if they were not new or you got ripped off with some crap kits from EBAY.
No biggy if the valves are new and good, you will be adjusting and checking it anyway.
Set your calipers to the figure quote and to work with your float weight, check they are accurate with a ruler or micrometer and proceed to tweak the float, if needed, this is to obtain the correct figure at the floats furthest extremity (A) from the needle valve.
As shown below in other images, to adjust the float level tweak the floats.
(see dhlafloatlevel)
As seen below. It helps to hold the carb top vertically or just off vertical unless you are an octopus. This is so the float tab rests naturally against the needle valves rounded tip.
This MUST be done with the top plate gasket in place.
(see floatinitial)
Most people just finish here and call that setup. This is just stupid, as it often does not translate into a good fuel level in the carb. Depending on if metal or viton tipped needle valved are used and also the valve body can be No1 or No2, floats may have been "butchered" by previous "engineers".
So this is where my technique starts. I use the above info ONLY for reference and initial setup to start off the correct adjustment.
After the above is done, if the carburettors are not bolted to the car, fit them now, but do not fit the top linkage or filters, as you will be removing the float covers and floats and will need to look down the barrels for leaking.
Before adding the fuel pipes to the carbs test the fuel pressure first.
Set at 3psi if using metal valves and up to 5psi if using viton.
Once this is set, fix the fuel pipes to the carbs but do not fill the bowls or operate the electric pump yet. (I hope you are using one!)
Its important to do this on the car, as different fitments/manifolds give a different "angle" or rake to the carb, the main-jet stack must be supplied with a proper fuel level.
Firstly remove two of the top plate cover screws, so each top plate (float cover) is being held down with only two screws.
Below image shows why is it important to leave two screws in place till you are "perfected" in your technique here...
The choke plunger will spring the top plate upwards with no screws in place, so giving a poor reading and leakage if you allow this to happen at any time during this calibration.
Its VERY important to keep the float cover sat firmly on the carb at all times when setting the "fuel bowl levels" ~ to the all important setting so often ignored through ignorance or naivity.
(see top1)
Below shows where the top needs to be while the pump is filling, down on the mating surface, also it needs to be here all the time, till you quickly WHIP it off to check the fuel level.
(see top2)
The gasket needs to be under compression too.
(see caliper27mm)
Get your caliper and set to 27mm!!!!!!!! check the pointy end you will be using is actually set to 27mm in length with a ruler or micrometer and that its accurate to 0.5mm.
You are now ready to fill the fuel bowls. So flick on the pump...Wait for 20seconds. Flick it off, look down inside the barrel into the venturi, if you can see fuel dripping from the venturi the bowl has a bit too much fuel in or you valve is worn if they were not new or you got ripped off with some crap kits from EBAY.
No biggy if the valves are new and good, you will be adjusting and checking it anyway.