bigger jets for nikki?
10-10-03, 03:19 PM
#6
Nikki-Modder Rex-Rodder
Join Date: Feb 2001
Location: Trying to convince some clown not to put a Holley 600 on his 12a.
Posts: 2,890
Likes: 0
Received 13 Likes
on
6 Posts
You mention a few different cars in your sig, so I don't know what the application is. What kind of exhaust, and what fuel delivery?
10-14-03, 10:54 AM
#7
Full Member
Join Date: Jun 2002
Location: Western Australia
Posts: 70
Likes: 0
Received 0 Likes
on
0 Posts
Sorry to drag up an old thread but it never got an answer. I was wondering about doing the same thing to myself.
I have a 12A carby on a S4 turbo block (straight through exhaust, no emissions, 2nd gen ignition and pod filter) and was wondering how i can increase the size of the jets. I have heard that the primary jet can be increase 1 size and the secondary 2 sizes, I don't know if this is true.
Orig Jet sizes
Primary 93 (=0.93mm???)
Secondary 160 (=1.60mm???)
I have been told to just drill them slightly bigger but exactly how much and if we are talking in the hundreths of a mil wouldnt that be quite hard?
I have a 12A carby on a S4 turbo block (straight through exhaust, no emissions, 2nd gen ignition and pod filter) and was wondering how i can increase the size of the jets. I have heard that the primary jet can be increase 1 size and the secondary 2 sizes, I don't know if this is true.
Orig Jet sizes
Primary 93 (=0.93mm???)
Secondary 160 (=1.60mm???)
I have been told to just drill them slightly bigger but exactly how much and if we are talking in the hundreths of a mil wouldnt that be quite hard?
Trending Topics
10-14-03, 10:21 PM
#9
Nikki-Modder Rex-Rodder
Join Date: Feb 2001
Location: Trying to convince some clown not to put a Holley 600 on his 12a.
Posts: 2,890
Likes: 0
Received 13 Likes
on
6 Posts
The stock Nikki as found on a manual transmissioned Rx-7 has the following jet sizes in inches (sorry VaSSagO - we're too pigheaded in this country to get on the metric scale like everyone else on Earth) :
Primary fuel jet- .036, primary air jet- .028
Secondary fuel jet- .063, secondary air jet- .055
This is what you could do on a stock carb regarding jets, and it's about the most fuel you can meter thruogh it given its flow of only 313 CFM (courtesy of the Banana).
If you're leaving vacuum secondaries:
Drill the primary fuel jet out to .050, but leave the secondary fuel jet alone.
Lead up the secondary air jet and redrill to .045
If you're converting to mechanical secondaries:
Drill the primary fuel jet out to .045, and leave the secondary fuel jet alone.
Lead up the secondary air jet and redrill to .040
Now there's a problem with leading the emulsion tube air jets. They are assembled by being soldered in the first place, so if you're not careful, you can cause problems. It's also very easy for the molten solder to be sucked into the tube, filling it or coating the inside, thus changing the diameter of the emulsion tube, as well as its crossdrilled holes. This will alter it's characteristics, and it won't function for ****.
There's no sense in opening the secondary jet because at the CFMs of the stock carb @ WOT, you should be getting plenty rich of a mixture. The smaller air jet in the secondaries will insure that the main circuit sees more vacuum at WOT. The combination of opened primary fuel jets and opened up secondary fuel jets would deliver too much fuel for the CFMs in the midrange, and the extra rich condition will kill power.
The most dramatic effect for acceleration will come by changing the carburetor from vacuum operated secondaries to mechanical. This, along with a modification to increase accelerator pump volume and stroke, will make a big difference in feel.
All of these things WILL have a noticeable effect on your wallet, too. Mileage is gonna suffer if ya wanna go faster.
The mech. secs. mod and AP mod can be found HERE .
When Carl or I do a SterlingCarb, it flows 37% more than a stock Nikki. Though the fuel jets can be swapped out easily for tuning, the air jets are fixed orifices in the emulsion tubes. We drill out the Etubes and thread them to accept jets with the same thread pitch as the fuel jets.
It is this air "jettability" that makes our modded carburetors so tunable to your needs. You can tune the carb to deliver richer or leaner at any given RPM band.
For example; For race application where the RPMs are high most of the time, you want the mixture to be as lean as you can have it up top and still make "moving power". If you have the carb tuned for "accelerating power", it's running too rich, you're using up all your fuel, and where in the RPMs is going to accelerate to?
You want the midrange to be your "accelerating power" range, and so that gets tuned to be richer.
For the street, you might want a lean, "moving power" mixture delivered for highwat cruising, but have "acceleration power" in the mid and upper RPM band. Mechanical secondaries helps with this immensly, because you don't always want a rich mixture in the mid or top, and this can be achieved by only climbing at partial throttle.
The air jets usually come into play high in the RPMs, depending on the float drop setting. Changing to smaller air jets will cause less of the vacuum signal to be bled off at high RPMs, thus richening the mixture. The maximum is met by the choice of fuel jet size.
It's for this reason that the high RPM tuning should be done last.
Visit Paul Yaws site for more on tuning.
Primary fuel jet- .036, primary air jet- .028
Secondary fuel jet- .063, secondary air jet- .055
This is what you could do on a stock carb regarding jets, and it's about the most fuel you can meter thruogh it given its flow of only 313 CFM (courtesy of the Banana).
If you're leaving vacuum secondaries:
Drill the primary fuel jet out to .050, but leave the secondary fuel jet alone.
Lead up the secondary air jet and redrill to .045
If you're converting to mechanical secondaries:
Drill the primary fuel jet out to .045, and leave the secondary fuel jet alone.
Lead up the secondary air jet and redrill to .040
Now there's a problem with leading the emulsion tube air jets. They are assembled by being soldered in the first place, so if you're not careful, you can cause problems. It's also very easy for the molten solder to be sucked into the tube, filling it or coating the inside, thus changing the diameter of the emulsion tube, as well as its crossdrilled holes. This will alter it's characteristics, and it won't function for ****.
There's no sense in opening the secondary jet because at the CFMs of the stock carb @ WOT, you should be getting plenty rich of a mixture. The smaller air jet in the secondaries will insure that the main circuit sees more vacuum at WOT. The combination of opened primary fuel jets and opened up secondary fuel jets would deliver too much fuel for the CFMs in the midrange, and the extra rich condition will kill power.
The most dramatic effect for acceleration will come by changing the carburetor from vacuum operated secondaries to mechanical. This, along with a modification to increase accelerator pump volume and stroke, will make a big difference in feel.
All of these things WILL have a noticeable effect on your wallet, too. Mileage is gonna suffer if ya wanna go faster.
The mech. secs. mod and AP mod can be found HERE .
When Carl or I do a SterlingCarb, it flows 37% more than a stock Nikki. Though the fuel jets can be swapped out easily for tuning, the air jets are fixed orifices in the emulsion tubes. We drill out the Etubes and thread them to accept jets with the same thread pitch as the fuel jets.
It is this air "jettability" that makes our modded carburetors so tunable to your needs. You can tune the carb to deliver richer or leaner at any given RPM band.
For example; For race application where the RPMs are high most of the time, you want the mixture to be as lean as you can have it up top and still make "moving power". If you have the carb tuned for "accelerating power", it's running too rich, you're using up all your fuel, and where in the RPMs is going to accelerate to?
You want the midrange to be your "accelerating power" range, and so that gets tuned to be richer.
For the street, you might want a lean, "moving power" mixture delivered for highwat cruising, but have "acceleration power" in the mid and upper RPM band. Mechanical secondaries helps with this immensly, because you don't always want a rich mixture in the mid or top, and this can be achieved by only climbing at partial throttle.
The air jets usually come into play high in the RPMs, depending on the float drop setting. Changing to smaller air jets will cause less of the vacuum signal to be bled off at high RPMs, thus richening the mixture. The maximum is met by the choice of fuel jet size.
It's for this reason that the high RPM tuning should be done last.
Visit Paul Yaws site for more on tuning.
Last edited by Sterling; 10-14-03 at 10:30 PM.
10-15-03, 10:20 AM
#11
Nikki-Modder Rex-Rodder
Join Date: Feb 2001
Location: Trying to convince some clown not to put a Holley 600 on his 12a.
Posts: 2,890
Likes: 0
Received 13 Likes
on
6 Posts
Originally posted by Rx7carl
Stock is 297 CFM. Whered you get 313?
Stock is 297 CFM. Whered you get 313?
I sent you back the chart just now.
Ill have to look when I get home. 
09-02-04, 08:03 AM
#14
Nikki-Modder Rex-Rodder
Join Date: Feb 2001
Location: Trying to convince some clown not to put a Holley 600 on his 12a.
Posts: 2,890
Likes: 0
Received 13 Likes
on
6 Posts
This thread specifically pertains to a STOCK NIKKI CARBURETOR! This is assumed to be on a STOCK EXHAUSTED 12A ENGINE, as well.
So I gave out jet sizes, and used what little knowledge of the flow of the 12a rotary I have, along with Carl's flow bench findings of the the stock Nikki carb to arrive at some very basic conclusions, which I laid down as my jetting suggestions.
So what happens with fuel from a state that requires 10% ethanol? That means that with two people in different states with ABSOLUTELY IDENTICAL CARS AND WEATHER CONDITIONS will need different jetting configurations, no?
How about one's whose *** has fifteen more pounds on it?
One has a crack in his main cat honeycomb.
One's average temperature is 12* higher daily for 3 more hours than the other.
One chooses 40 wieght instead of 30 weight oil.
THE LIST OF VARIABLES IS INFATHONABLY LONG!
So I gave out jet sizes, and used what little knowledge of the flow of the 12a rotary I have, along with Carl's flow bench findings of the the stock Nikki carb to arrive at some very basic conclusions, which I laid down as my jetting suggestions.
So what happens with fuel from a state that requires 10% ethanol? That means that with two people in different states with ABSOLUTELY IDENTICAL CARS AND WEATHER CONDITIONS will need different jetting configurations, no?
How about one's whose *** has fifteen more pounds on it?
One has a crack in his main cat honeycomb.
One's average temperature is 12* higher daily for 3 more hours than the other.
One chooses 40 wieght instead of 30 weight oil.
THE LIST OF VARIABLES IS INFATHONABLY LONG!
Last edited by Rx7carl; 09-04-04 at 10:21 AM.
09-02-04, 12:28 PM
#16
Airflow is my life
Now that I have trimmed off the thread, its once again open. cdrad51, my suggestion to you is not to jumble up this thread with your setup. Greg was talking about stock carb on a stockport engine. Your posts would then confuse people (I was confused at first as to what was going on). Like Sterling mentioned, you cant compare apples and oranges, its just too confusing. Start a new thread about your specific setup so it can have its own place. People who actually search will find these threads much more helpful when they arent full of different setups and contradictions. Its very frustrating to those who try to help and post relavent info, to have it jumbled up like this.
Last edited by Rx7carl; 09-04-04 at 10:32 AM.
09-04-04, 01:46 PM
#19
Lorem ipsum dolor sit ame
Originally Posted by Rx7carl
Now that I have trimmed off the thread, its once again open. cdrad51, my suggestion to you is not to jumble up this thread with your setup. Greg was talking about stock carb on a stockport engine. Your posts would then confuse people (I was confused at first as to what was going on). Like Sterling mentioned, you cant compare apples and oranges, its just too confusing. Start a new thread about your specific setup so it can have its own place. People who actually search will find these threads much more helpful when they arent full of different setups and contradictions. Its very frustrating to those who try to help and post relavent info, to have it jumbled up like this.
09-04-04, 06:35 PM
#23
Nikki-Modder Rex-Rodder
Join Date: Feb 2001
Location: Trying to convince some clown not to put a Holley 600 on his 12a.
Posts: 2,890
Likes: 0
Received 13 Likes
on
6 Posts
That's alright, cdrad. I'll buy you the beer. 
-And don't worry, folks. There'll be plenty more times for me to go Postal and chance being banned.
-And don't worry, folks. There'll be plenty more times for me to go Postal and chance being banned.
09-04-04, 06:55 PM
#24
Lorem ipsum dolor sit ame
Originally Posted by Sterling
That's alright, cdrad. I'll buy you the beer.
-And don't worry, folks. There'll be plenty more times for me to go Postal and chance being banned.
-And don't worry, folks. There'll be plenty more times for me to go Postal and chance being banned.
09-04-04, 07:12 PM
#25
Nikki-Modder Rex-Rodder
Join Date: Feb 2001
Location: Trying to convince some clown not to put a Holley 600 on his 12a.
Posts: 2,890
Likes: 0
Received 13 Likes
on
6 Posts
I never said I was any kind of guru. (I really hate that!)
I never called you a "moron". -I just asked if you were one.
And I never called you a "jerk", either. I asked why you were acting like one.
But on every account, I'm sorry. And I will buy you the beer(s) I owe you.
I never called you a "moron". -I just asked if you were one.
And I never called you a "jerk", either. I asked why you were acting like one.
But on every account, I'm sorry. And I will buy you the beer(s) I owe you.