Quadrajet Question

DorianL

solid fixture here in the forum
Staff member
hey all,

I got a good hot idle. Vacuum is high. But left idle screw has no effect...

Any suggestions?

MTIA

D.
 
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It would be easier if both screws were ineffective, then It could be several things.
Check to make sure the correct base gasket is used.
Did you check for any vacuum leaks?
Could be a sticking or dirty power valve
 
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Yep. Indeed. It's odd that one screw is very responsive but not the other.

I could find no vacuum leaks. There was strong vacuum when I seat-of-pants checked... thumb in a vacuum hose. I used a phenolic spacer gasket.

I like the idea of blowing out the idle screw hole with compressed air and carb cleaner. Might be some time before I see Little Buddy's 'vette tho. Even longer before I can get him to come over to blow out the carb with my compressor
 
There is also the Milwaukee carb clean, not sure how it got the name.

With one hand rev the Engine and the other close the choke.

Don't let the Engine stall, but choke it fully as long as possible.

Open choke and let Engine normalize.

Repeat a couple of times.

Often the high vacuum created by the revving Engine with the choke closed will remove dirt from the idle circuit.

Thanks
Randy
 
I had the same problem with an electronic quadrajet.
I can't find a good picture on the internet to help.
With the mixture screw removed, shoot the carb cleaner into the tiny holes
near the booster cluster also. If you have to remove the air horn, then you can get to all the passages.
Let it sit for a few minutes to dissolve the crud, then blow out with compressed air.

4802-w-infol.gif qjet.jpg 0900c15280052780.gif
 
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This is why I leave parts sitting in a warm bath of solvent in an ultra sonic machine. It's really not a lot of money and really works.
 
Thanks Gentlemen.

Fantastic feedback. I'll let you know how it works out as soon as I have the opportunity to try it.

I did soak my carb in solvent for a couple of days. I suspect carb cleaner isn't what it used to be.

One more detail I forgot to add... That idle screw seems to wobble a bit loosely in its threads.

If air were leaking in that way surely it's minimal and closing it fully would still shut off the flow of gas stalling the engine.

The idle screw looked all right. But I've read that you can damage the seat (tho this is a loose wobble) perhaps not stopping the flow.

Hmmm. Best is to blow out the holes first and do the Milwaukee carb clean. Disassemble and start over if no result
 
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nozzle.gif


carbcleanery.jpg


http://garage.grumpysperformance.com/index.php?threads/carb-cleaning.12303/#post-60519
 
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Hey Guys,
I'm stuck and could use some help.
Just finished putting together top end on 88 sbc 350 w 906 Vortec heads, comp cam 12-231, performer intake, original(rebuilt) QJ carb. Original bottom end. Engine fired right up, set idle to 2000 for 20 minutes to break in cam, slowed idle to 800, set timing(12). Engine was running great, then it wasnt... Engine is now running very RICH, I mean that it fouls new plugs in 5 minutes or so and dies. Fuel vapor coming from tailpipes. Very rough idle. Idle mixture screws out 1 turn. I don't know what the heck happened. Any idea on where to start, what to check, etc... Thanks!

your stated symptoms suggest fuel pressures too high,
as usuall , issolate and test carefully!
GET A FUEL PRESSURE GAUGE AND MEASURE DON,T GUESS
how can you possibly set up your fuel system unless you know the pressure and flow rates required and what currently exist's
vgauge.gif


or needle valve controlling fuel flow into the carb, is jammed open
or floats are incorrectly set.





READ LINKS

http://garage.grumpysperformance.com/index.php?threads/setting-up-your-fuel-system.211/

http://garage.grumpysperformance.com/index.php?threads/fuel-pressure-regulators.635/

http://garage.grumpysperformance.com/index.php?threads/how-big-a-fuel-pump-do-you-need.1939/

http://garage.grumpysperformance.co...ss-fuel-pressure-regulators.12776/#post-65998
 
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