Q Jet Problem

[jimmyjack]

OK I finally found a used Q Jet to take the place of my edlebrock carb. The guy I got it from said it ran like a champ on his truck when he took it off. Only he didn't tell me is he took it off 3 yrs ago. It was sealed in a bag so it was nice and clean. I slapped it on and it fired up after just a few cranks. It runs great, but it idles around 2000 RPMs and it won't back off. I tried to turn out the idle screw, nothing. I played with the A/F screws, nothing. I turned the hi idle screw, nothing. No leaks, everything is hooked up. Whattaya think? I'm stumped. I don't know SQUAT about carbs

 

[fatbob]

Here's some links for ya.
http://www.florida4x4.com/tech/quadrajet/
I would first check for vacuum leaks. But they do mention in one of those links
that the plugs in the bottom of the bowl are known to leak. That COULD be giving the motor the extra gas .

 

[akbound]

I looked at my Haynes Rochester Carb manual and the only thing that I thought of was the fast idle adjustment. I would suggest you get one of these, they are about $15 at AutoZone IIRC.

Also, from the link the previous replyer sent here is a quote:

Fast idle screw incorrectly adjusted​

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Results in: ​

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Initial cold-startfast idle too high or too low.
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Comments: ​

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The fast idle screw is hidden so well that many people don’t know it even exists. The screw is located
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under the choke linkage on the passenger side of the car. The screw head faces forward. Fast idle speed should be
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adjusted to about 1200 rpm on a cold engine.​

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I hope this helps.​

 

[GMCLegacy]

check to see if your secondaries are slighlty opened, i have had that happen one before after sitting un-used for a while.

what style choke is on the carb? the high idle for the choke may be stuck.

do you have all the vacuum ports in use or plugged?

 

[jimmyjack]

I think I have it narrowed down to the choke. I turned that hi idle screw about all the way out. Nothing changed. But I forcibly moved the throttle linkage forward and slowed down to about 700 rpm. When I did this I could see the choke linkage move a little. So I think the problem is in there. just gotta figure out what it's doing.

 

[jimmyjack]

I figured it out. I had a friend email a few pics of his. This carb on the blazer has the vacuum secondary on the front of the carb. My old one has the vac. sec. on the rear. Any carb I've ever owned has the vac. sec. on the back so I took it off the old junk carb and put it on the "new" carb . Well, they were fighting each other, bcos I had hooked the primary up as well. I ditched the old vac. pot and now it's normal. It still has a few hiccups cos I messed with the screws, but it's running really well considering. Thanks for the input guys!

 

[R72K5]

usually caused by the secondaries air valve flaps being open, but glad to see it was something obvious and minor

all the little fast idle choke cam parts have to work together just right, keep them cleaned and lubed, you knwo the adjusting screw under the choke assembly right ? it adjusts how fast engine runs when choke is shut and til about 3/4 open maybe little less


goo dluck