Quadrajet from hell will not give me peace

Slooptin

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So I recently rebuilt my q jet, mostly to do throttle shaft bushings, but also just to give myself peace of mind that everything was actually done right when I rebuilt it the first time. Well now it's worse, and I'm not ruling out rebuilder error on my part, I just don't even know what's going on and this is my daily so its starting to stress me out.

When I turned on the truck this morning, it rev'd up to about 1600 rpm which is normal, but my afr was reading 9. I went to blip the throttle and nothing changed. I thought ok, sometimes it takes a second so I blipped it again and nothing. Threw it into gear to see if that would normal things out and it only dropped to 1200 rpm, afr still at 9. Called it quits and got a ride from my wife.

This is after me trying to get it to work this weekend where, similar thing happened, I turned on the truck and it rev's up to 3000 rpm. when that happened. I had more time to mess with it and no change in the idle set screw or idle air/fuel meter screws made any difference in the rpm. The weird thing is that it only does this high revving stuff sometimes. Sometimes I'm able to start the truck up and it's completely normal.

My brain is pointing toward it running off the secondaries and I notice (for the first time, this wasn't something i paid attention to before) that after pushing the throttle in to set the choke, the secondary throttle blades seem to be open just a little. They seem to stay that way during normal idle (normal rpms) and when i tried to close them by hand, the truck stalled like it was starving for air. I'm confident I reinstalled the secondary throttle return springs correctly and I've looked at them a million times to ensure i didn't screw it up.

IDK guys, I'm close to tossing this q jet in the trash and throwing on the autozone edelbrock carb just to have something that works because this one doesn't
 

Designo614

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I'm in a G-body group for my '87 El Camino, which came stock with a 305 with a Rochester Quad. I have seen many people comment that Mountain Man Fuel Systems is the guy to send your Quadrajet to for a professional rebuild:

 

Originalthor

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I've rebuilt a few good old q jets in day. My first one i forgot to put in that little ball or it fell out while assembly. One i put in wrong kit to carb. Oops. Just some things I've screwed up on that maybe your problem.

Next few were money even did a few carters in there. Then one I just found it plane worn out if that makes any sense now matter what I did I couldn't get to run right. Tossed it and went to edelbrock. Still have that carb to this day.
 

fast 99

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When the shafts were re-bushed did you seat the throttle plates in the bores? I usually do that holding the base plate up to a strong light. Could the throttle shaft have a twist in it? In order for the engine to rev like that it needs air and fuel from somewhere. Is the fast idle cam all the way down? Vacuum leak? Were the internal gaskets matched up? This isn't a usual Q-jet issue.
 

Slooptin

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When the shafts were re-bushed did you seat the throttle plates in the bores? I usually do that holding the base plate up to a strong light. Could the throttle shaft have a twist in it? In order for the engine to rev like that it needs air and fuel from somewhere. Is the fast idle cam all the way down? Vacuum leak? Were the internal gaskets matched up? This isn't a usual Q-jet issue.
not sure about seating throttle plates in bores. fast idle cam is down, no vac leaks, gaskets matched the old ones I took out. I don't think the shaft has a twist in it. it went in the same way it came out
 

fast 99

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If the throttle plates leak air the motor will rev. Hate to say it but need to check that. Only good way is to remove the base plate. When re-bushing install the screws somewhat loose using blue locktite or fingernail polish and close the shaft. Lightly tap on the plates with the handle of a screwdriver to seat them, hold the throttle closed, tighten the screws. The plates have a top and bottom. Usually the top has slight grid pattern. Re-check that they close completely without force.
 

Bextreme04

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It honestly sounds like a choke issue. Can you post some pics of what you have going on with both sides of the carb? What kind of choke does it have? Did you reset everything to the proper starting point after the rebuild? What kind of choke does it have now? When the choke is properly applied on a cold engine, it should have a lock out tab on the passenger side that keeps them from opening.
 

Slooptin

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Ok, well i was able to tear the carb apart last night and i guess it was a user error. the bushings I installed for the secondaries were way too tight. I was able to drill them out enough to where the shaft was able to move freely without any play and with the spring installed, the blades could snap back into place. I'll see if that makes the difference
 

Octane

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Unless one is especially good with a qjet, a new Holley is the best answer to the problem. Install,tweek and done. Imho.And I've done many rebuilds of qjets successfully.But hands on analysis works best for me.
 

fast 99

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A few here seem to think the answer to a q jet problem is a Holly. Yes, I have been unable to fix a few q-jets. However, I have probably tossed out more Holleys. Couple things, if a piece of crud gets in a Holley valve body sometimes it can't be removed, it is junk. With age they leak. An over-the-counter Holley is generic. Designed to work just ok on everything. The original q-jet is designed to work on that particular application. Fuel and choke rates are closer to what that vehicle requires. Holley's are easier to work on and parts are everywhere, but they aren't a cure all. Converting to a Holley can be more time consuming than actually fixing the Q-jet and will cost $400 or more. Also, down the road it will usually take more time to rebuild a Holley that a Q-jet.

Forgot to mention that pesky power valve in Holleys. 1 backfire it could fail.
 
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Mr. Goodtool

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I had this exact problem with my qjet. I had used a 1/4x20 nut on top of the air cleaner stud, just above where it screwed into the top of the carburetor, to secure the stud. The sides of the nut would catch on the secondary cam every so often, and the fix was to just leave the nut off. I was overthinking the securement of the stud. The Factory threads were fine. I learned this the hard way, in traffic, but no damages luckily.
 

Conejo_K10

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The only thing I don't like about Q-jets is the air horn [or top] is too thin. They warp easily unless you're very cautious with the bolt torque.
If they're warped the fuel bowl will leak into the primaries. I always check mine with a straight edge. If they are warped I've had luck lap filing them.
Of course they wear out and are not east to find for a specific part number carb.
 

Matt69olds

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The air horn screws inside the choke tower (the tapered ones) need to be tightened first. Those locate the air horn on the main body. If the other screws are tightened first, that can cause problems.
 

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