vacuum advance with a dellorto
02-24-07, 09:56 AM
#1
vacuum advance with a dellorto
well im installing a dellorto 48 on the DD today. i have a concern, the vacuum advance. i know its debatable if you need it or not. i know the advantages are better gas milage and maybe a little performance, but arent *needed*. i have the same setup on my SP 13b in my project car without the advance hooked up. id like to run it on my DD though. one question, when drilling the hole for the tap, would it be better in a primary or secondary port? i also plan on playing with the timing a little today for the first time. maybe be figure out a good setting for a little more go, and then use stock for better ecomony. any input is appreciated. thanks.
02-24-07, 11:50 AM
#2
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I recommend keeping vac advance. Your car will run like shiz without. And as far as performance goes, your not going to notice anything significant. So just time it to the recommended timing.
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02-24-07, 02:11 PM
#8
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Originally Posted by aws140
but where does the advance need to be hooked up, primary or secondary?
Venturi vacuum is found above the throttle plates. As the flow increases thru the venturis, due to the throttle plates opening, the advance will start to get it's vacuum, and thereby advance the timing as the engines load increases.
02-24-07, 03:47 PM
#9
RicanRider
Originally Posted by aws140
well im installing a dellorto 48 on the DD today. i have a concern, the vacuum advance. i know its debatable if you need it or not. i know the advantages are better gas milage and maybe a little performance, but arent *needed*. i have the same setup on my SP 13b in my project car without the advance hooked up. id like to run it on my DD though. one question, when drilling the hole for the tap, would it be better in a primary or secondary port? i also plan on playing with the timing a little today for the first time. maybe be figure out a good setting for a little more go, and then use stock for better ecomony. any input is appreciated. thanks.
I have my 45DCOE on a 12A SP with the vacum advance disconnected. Plugged the vacum and advance the ignition timming by about 5degrees.....
It's been working great....
02-24-07, 04:01 PM
#11
Originally Posted by Rogue_Wulff
Actually, neither. The vacuum advance needs to hooked to a venturi vacuum, that only draws vacuum when the throttle is opened. Not manifold vacuum.
Venturi vacuum is found above the throttle plates. As the flow increases thru the venturis, due to the throttle plates opening, the advance will start to get it's vacuum, and thereby advance the timing as the engines load increases.
Venturi vacuum is found above the throttle plates. As the flow increases thru the venturis, due to the throttle plates opening, the advance will start to get it's vacuum, and thereby advance the timing as the engines load increases.
02-24-07, 05:32 PM
#12
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Originally Posted by trochoid
Give the man a cigar!!!
Originally Posted by trochoid
Manifold vacuum drops when the throttle plates open. Ever watch a vacuum gauge on a running engine?
02-24-07, 06:34 PM
#13
Originally Posted by aws140
well, since i cant decide where to put it, i wont be running it. doesnt matter now. due to crappy OMP lines i have to wait till i can get replacements before i can run the car.
02-24-07, 07:48 PM
#14
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Originally Posted by Frostycrowd
You all are crazy. Your crippling your cars performance(slightly) and economy, simply because you are to scared to hook a vac line up
With good reason. If not done correctly, you can seriously damage your engine. As my dumb *** proved. It isn't worth it if you are'nt 100% positive on the proper way to run it.
02-24-07, 11:44 PM
#15
Originally Posted by Rogue_Wulff
Actually, neither. The vacuum advance needs to hooked to a venturi vacuum, that only draws vacuum when the throttle is opened. Not manifold vacuum.
Venturi vacuum is found above the throttle plates. As the flow increases thru the venturis, due to the throttle plates opening, the advance will start to get it's vacuum, and thereby advance the timing as the engines load increases.
Venturi vacuum is found above the throttle plates. As the flow increases thru the venturis, due to the throttle plates opening, the advance will start to get it's vacuum, and thereby advance the timing as the engines load increases.
where would you sudjest the nipple be places on a set up like this then? you dont have very many options.
Originally Posted by Jeezus
i have some omp lines if you want, free +shipping
02-25-07, 12:58 AM
#16
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The nipple needs to be on the carb. Unfortunately, some sidedraft carbs do not have this made into them, as they are originally designed for racing, and most racers are more interested in where the total advance falls at XXXXRPM, and don't need the extra help down low in the RPM range.
Look your carb over, and see if there is an existing vacuum port on the throttle plate, or near it. Once (or if) you find one, check to see if it pulls vacuum at idle. A venturi vacuum port will pull little to no vacuum at idle, but once you start to open the throttle, it will start to pull more vacuum. If you find a port that matches this behaviour, thats the one for the advance. Just use a "T" to hook up both pods.
Look your carb over, and see if there is an existing vacuum port on the throttle plate, or near it. Once (or if) you find one, check to see if it pulls vacuum at idle. A venturi vacuum port will pull little to no vacuum at idle, but once you start to open the throttle, it will start to pull more vacuum. If you find a port that matches this behaviour, thats the one for the advance. Just use a "T" to hook up both pods.
02-25-07, 01:18 AM
#17
^^ill check tomorrow, but im 99% sure one doesnt exist on the carb. the only nipples already available is the one on the manifold for the brake booster, the OMP nipples, and one in the filter plate(probably use for PCV connection.
02-25-07, 01:21 AM
#18
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Do you have the original RB instructions for your Dell? I'm pretty sure it instructs to leave the vacuum ports disconnected. And, I don't think you're supposed to cap them, rather leave them open to the air. I can't remember the rationale, but I recall that capping them could lead to undesirable or erratic timing for some reason. You might want to do a search on this issue. Personally, I left mine disconnected and uncapped and never had any problems with it.
02-25-07, 01:24 AM
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I just remembered this. I have seen a couple sidedrafts carbs that had a threaded hole with a plug in them. This *may* be for the vac. advance, if so desired.
Check the OMP nipples, if they act in the correct manner, you could use one of those, and make new nipples in the intake for the OMP hoses, or just go to premixing.
Check the OMP nipples, if they act in the correct manner, you could use one of those, and make new nipples in the intake for the OMP hoses, or just go to premixing.
02-25-07, 02:44 AM
#20
Originally Posted by SilverRocket
Do you have the original RB instructions for your Dell? I'm pretty sure it instructs to leave the vacuum ports disconnected. And, I don't think you're supposed to cap them, rather leave them open to the air. I can't remember the rationale, but I recall that capping them could lead to undesirable or erratic timing for some reason. You might want to do a search on this issue. Personally, I left mine disconnected and uncapped and never had any problems with it.
Originally Posted by Rogue_Wulff
I just remembered this. I have seen a couple sidedrafts carbs that had a threaded hole with a plug in them. This *may* be for the vac. advance, if so desired.
Check the OMP nipples, if they act in the correct manner, you could use one of those, and make new nipples in the intake for the OMP hoses, or just go to premixing.
Check the OMP nipples, if they act in the correct manner, you could use one of those, and make new nipples in the intake for the OMP hoses, or just go to premixing.
02-25-07, 10:38 AM
#21
Originally Posted by SilverRocket
Do you have the original RB instructions for your Dell? I'm pretty sure it instructs to leave the vacuum ports disconnected. And, I don't think you're supposed to cap them, rather leave them open to the air. I can't remember the rationale, but I recall that capping them could lead to undesirable or erratic timing for some reason. You might want to do a search on this issue. Personally, I left mine disconnected and uncapped and never had any problems with it.
Originally Posted by trochoid
The vacuum pots are left uncapped so the advance can work. Capping them off will prevent the normal internal advance.
On the Mikunis for the 12As, there's a nipple in each barrel. On the SE carbs, those nipples are plugged. I would need to look at mine to see if they are before or after the butterflys. I think they are after
On the Mikunis for the 12As, there's a nipple in each barrel. On the SE carbs, those nipples are plugged. I would need to look at mine to see if they are before or after the butterflys. I think they are after
slacking
i was wondering how long itd take you to show up
so what advice do you have for me? ill check my carb today and see what i can find.
02-25-07, 12:36 PM
#22
heres what i found. i dont know what these are for. maybe theyll work?
the way the holes are one hole is after the butterfly when the throttle is closed and as the throttle progresses to open more holes are behind the butterfly.
i looked in my "how to build and power tune weber and dellorto" book and it says that screw is for a progression hole. when i looked to see what its for it says, "the cover was put there in the first place to allow for the progression holes to be drilled but it also doubles as a removeable plug for cleaning purposes.."
the way the holes are one hole is after the butterfly when the throttle is closed and as the throttle progresses to open more holes are behind the butterfly.
i looked in my "how to build and power tune weber and dellorto" book and it says that screw is for a progression hole. when i looked to see what its for it says, "the cover was put there in the first place to allow for the progression holes to be drilled but it also doubles as a removeable plug for cleaning purposes.."
Last edited by dbragg; 02-25-07 at 12:51 PM.
02-25-07, 12:53 PM
#24
Originally Posted by Rogue_Wulff
That screw-in brass nipple,in the 3rd pic, is that just above the throttle plates?
02-25-07, 01:00 PM
#25
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Ah, on the other end. It was so close up, I couldn't tell if that was throttle plate, or choke. Had it been throttle plates, it woulda been perfect.......
It may be too high to pull a proper venturi vacuum. I'm guessing the other nipple in that pic is the OMP port, and has a matching one on the other barrel. Also looks too far away from the throttle plates to pull a proper venturi vacuum.
It may be too high to pull a proper venturi vacuum. I'm guessing the other nipple in that pic is the OMP port, and has a matching one on the other barrel. Also looks too far away from the throttle plates to pull a proper venturi vacuum.