nikki jetting
Thread Starter
Joined: Nov 2001
Posts: 951
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From: Las Cruces, NM
nikki jetting
I have read on yaws site how to jet a carb and understand it ok. But what sizes should i start from? I know if i am running rich in midrange i should swap 1 size blah blah etc., But where do i start?
Nikki-Modder Rex-Rodder
Joined: Feb 2001
Posts: 2,890
Likes: 14
From: Trying to convince some clown not to put a Holley 600 on his 12a.
First you need to tune the accelerator pump. Do it in 1/4 turn increments, and drive it each time. (Load conditions as opposed to in your driveway.)
Once you have that, and your mixture, and your idle, and your float drop, and your fuel pressure all set, you can tune the jetting.
Unfortunately, you need to have several sizes.
Start with the primaries. Put in one size bigger, drive it, smile, and repeat...untill you don't smile. Then go back one size to where you were smiling! You keep moving up untill you hit a size that's too big.
Now do the secondaries.
If you go back after the secondaries are set and make a change to the primaries, you may have to reset the secondaries again.
Removing the choke plate and shaft will help a little with flow. Every component, no matter how insignificant it seems, will interrupt air flow. The best you could do is remove what you can. Anything else requires full disassembly and machining.
You could also monkey around with airbleed configurations, but that won't do much for a stock Nikki.
After all that, you can convert the carb to mechanical secondaries, and do an accelerator pump volume increase.
I have a write up here on both if you look through the posts; or you can email me at dennisandmissy@mindspring.com
If I'm not mistaken, you already have a copy.
Are you drilling your own jets out? If so, use only brand new jewelers bits and bees wax. It'll make a clean hole and a sure diameter. Don't "ream" the hole by moving the bit in and out as this will make it larger and inconsistant. Hold the jet securely in a Jacobs chuck in a vice.
As far as sizes, I don't know. Paul sent me much larger than stock jets, but they are measured differently. Incrementally, they are only a few thousandths larger than each other.
Once you have that, and your mixture, and your idle, and your float drop, and your fuel pressure all set, you can tune the jetting.
Unfortunately, you need to have several sizes.
Start with the primaries. Put in one size bigger, drive it, smile, and repeat...untill you don't smile. Then go back one size to where you were smiling! You keep moving up untill you hit a size that's too big.
Now do the secondaries.
If you go back after the secondaries are set and make a change to the primaries, you may have to reset the secondaries again.
Removing the choke plate and shaft will help a little with flow. Every component, no matter how insignificant it seems, will interrupt air flow. The best you could do is remove what you can. Anything else requires full disassembly and machining.
You could also monkey around with airbleed configurations, but that won't do much for a stock Nikki.
After all that, you can convert the carb to mechanical secondaries, and do an accelerator pump volume increase.
I have a write up here on both if you look through the posts; or you can email me at dennisandmissy@mindspring.com
If I'm not mistaken, you already have a copy.
Are you drilling your own jets out? If so, use only brand new jewelers bits and bees wax. It'll make a clean hole and a sure diameter. Don't "ream" the hole by moving the bit in and out as this will make it larger and inconsistant. Hold the jet securely in a Jacobs chuck in a vice.
As far as sizes, I don't know. Paul sent me much larger than stock jets, but they are measured differently. Incrementally, they are only a few thousandths larger than each other.
I read your email
Joined: Jan 2002
Posts: 2,624
Likes: 1
From: NW New Jersey
I am clueless when it comes to carbs and this might be a basic question but: Where can different sized jets be purchased for the Nikki? Are jets universal or are they designed specifically for each carb? How can you tell what size jet is currently installed? TIA
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