Quadrajet air mixture screws - Team Camaro Tech
Troubleshooting Diagnosing problems done here.

 
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post #1 of 5 (permalink) Old Jun 14th, 02, 12:40 PM Thread Starter
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Join Date: Dec 2000
Location: Ontario Canada
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I am in the process of trying to tune my newly rebuilt 327 and Quadrajet carb. I currently have the timing, dwell and base idle set. I am now trying to adjust the air mixture screws. As I understand adjusting these screws will either increase or decrease the RPM and manifold vacuum. I can turn both screws in completly or out completly with no change to either RPM or vacuum pressure. Any ideas on what to look for?

[This message has been edited by Dan Trafford (edited 06-14-2002).]
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post #2 of 5 (permalink) Old Jun 14th, 02, 01:21 PM
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yeah...continue looking for no change. Mine is the same way. Apparently the design limits our ability to actually tune this feaeture. The book by Roe has a section on this and there are some threads either here or on the net that talk about making the necessary changes to accomodate the tuning of said screws. YOu need a numbered drill bit set to performance tune it. I believe (memory not working here) that the design was purposely too lean(or rich) to meet upcoming smog reqs and then it just kinda stuck around with no design changes. Mine is the same way?!
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post #3 of 5 (permalink) Old Jun 14th, 02, 04:51 PM
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sounds like you have the throttle blades open too far at idle. you aren't even actually using the idle circuit at all, that's why the screws make no difference at all.
what you need to do is turn the idle speed screw back a ways to bring the idle down, then pull the timing ahead a bit to bring the idle back up where it needs to be. the trick is finding the "sweet spot" where you have enough initial timing for a good idle and throttle response, but not so much that it pings itself to death or is hard to start when hot. this is where a custom distributor timing curve comes in handy.

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1971 Nova(looks like 69 camaro from underneath!)
355sb, vortec heads, HOT cam,T-10 tranny, 3.70 gears 16X8" IROC wheels. 12" Corvette brakes on the way.
see pics here http://community.webshots.com/user/novaderrik
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post #4 of 5 (permalink) Old Jun 15th, 02, 05:54 AM Thread Starter
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I will try to back off the idle screw and readjust the timing again. However the engine is running at 700 rpm's now I don't think I can go much lower then that. I also checked the manifold pressure and it reads about 11-13 inches of vacuum is this too low?
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post #5 of 5 (permalink) Old Jun 15th, 02, 07:43 AM
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you might get lucky and only have to back the idle screw off a little bit. make sure both the idle screws are 1.5 turns out from gently bottomed.keep the distributor loose enough to move it as you go- start with the timing. a few degrees forward, then turn the idle down. try the idle screws. keep doing it like that until it starts to work. the throttle blades should be damn near all the way closed when you are done.

------------------
1971 Nova(looks like 69 camaro from underneath!)
355sb, vortec heads, HOT cam,T-10 tranny, 3.70 gears 16X8" IROC wheels. 12" Corvette brakes on the way.
see pics here http://community.webshots.com/user/novaderrik
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