Tuning a Quadrajet
Thread Starter
Racer
Joined: Jun 2007
Posts: 291
Likes: 6
From: Delray Beach FL
Tuning a Quadrajet
I pulled the plugs on my motor and after about 300 miles and they look like the motor is running very rich. The problem is when I try to adjust the carb. I do not notice any significant changes in vacuum of rpm's when I turn the screws in or out. The Carb was rebuilt a few years ago.
Need some suggestions
Need some suggestions
Le Mans Master
Joined: Jan 2006
Posts: 9,192
Likes: 27
From: Boca Raton Florida
Sounds like some fat jets in there. What was your idle speed when you were trying to adjust?
Lars is the carb guru in here. He has a paper on Quad tuning. I'll see if I can find it, but someone else may pop in with it
I am in Boca by the way
Edit:
Here you go
http://www.lbfun.com/Corvette/Tech/v...ng%20Paper.pdf
Lars is the carb guru in here. He has a paper on Quad tuning. I'll see if I can find it, but someone else may pop in with it
I am in Boca by the way
Edit:
Here you go
http://www.lbfun.com/Corvette/Tech/v...ng%20Paper.pdf
Last edited by SIXFOOTER; Aug 9, 2007 at 11:35 AM.
Melting Slicks
Joined: Mar 2005
Posts: 2,838
Likes: 10
From: Austin TX
Those screws will only impact your idle mix. Agree, with the above,..if the plugs are sooty (new word) the primary jets may be too big and/or the rods too small. Do you know what's in it now? Is a stock set up?
Also, make sure your choke is in good working order.
Also, make sure your choke is in good working order.
Tech Contributor
Joined: Aug 1999
Posts: 14,380
Likes: 6,391
From: At my Bar drinking and wrenching in Lafayette Colorado
If the idle mixture screws have no effect and you can screw them all the way in without killing the engine it means you are idling on the main discharge system and not on the idle circuit. This can be caused by several things, starting with timing setup and ending with internal carb issues.
Start with checking timing and timing advance. You need to have a functional centrifugal advance system, and you need to be set up for 36 degrees total timing. Next, verify that the vacuum advance is functional (not ruptured) and that it's hooked up to manifold vacuum on the carb. Proper timing will assure proper meteing signal to the carb and will allow the lowest idle speed setting. A lower idle speed will activate the idle fuel circuit. If it doesn't, the carb will need some work to correct the fuel feed problem.
Start with checking timing and timing advance. You need to have a functional centrifugal advance system, and you need to be set up for 36 degrees total timing. Next, verify that the vacuum advance is functional (not ruptured) and that it's hooked up to manifold vacuum on the carb. Proper timing will assure proper meteing signal to the carb and will allow the lowest idle speed setting. A lower idle speed will activate the idle fuel circuit. If it doesn't, the carb will need some work to correct the fuel feed problem.
Thread Starter
Racer
Joined: Jun 2007
Posts: 291
Likes: 6
From: Delray Beach FL
The carb is the original one for the motor. I did not have it rebuilt it came on the motor. I will check the timing tonite. The vacuum advance does not seem to be getting any vacuum at idle do to the TCS valve.
