Quadrajet Questions
Thread Starter
Racer
Joined: Apr 2006
Posts: 340
Likes: 0
From: Warrensburg MO
Quadrajet Questions
1977..Rebuilt my QJet with the help of Lars info. Everything went great. Two things I have noticed. One is that I don't have a ported vacuum source on the carb. I have checked them all, and they all read manifold vacuum at idle. The second issue is that the lowest RPM I can achieve is 620; stop not touching setscrew. Is this OK? The only thing I see preventing further closure of the primaries is the linkage between the primaries and secondaries. I am pretty sure that there was a measurement in that area, and it checked out good (been awhile now since rebuild), but am wondering if these symptoms are normal? Also, the idle RPM I am referring to is in Park with vacuum to distributor plugged. I have driven the car for a few months now, and it runs well. Thanks.
TommyJ
TommyJ
Thread Starter
Racer
Joined: Apr 2006
Posts: 340
Likes: 0
From: Warrensburg MO
Melting Slicks
Joined: Nov 2001
Posts: 2,668
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From: Eastern US XX
Racer
Joined: Nov 2004
Posts: 485
Likes: 1
From: Oakville ON
I don't know if both kinds came on Vettes, but there are 2 kinds on Qjets: ported vacuum for control of EGR (no EGR at idle) and ported manifold vacuum for the distributer vac advance system. My '85 pontiac had both so it had full vac adv at idle and light cruise (the ported manifold signal was stronger than just manifold at cruise). This may have only been for Canadian cars though because our emissions limits were not the asame as in the US at that time.
My '78 Vette has an '85 carb with both.
My '78 Vette has an '85 carb with both.
Team Owner
Joined: Jan 2006
Posts: 37,637
Likes: 3,116
From: Crossville TN
It sounds to me like you have adjusted the throttle plates too far open so that the ported connections are already opened. If so, you have another problem in the carb. If you can turn the idle jets all the way in (closed) and the car still runs, there is an air leak into the intake (bad gasket, whatever) and that is forcing you to open the trottle to get adequate fuel mixture [and resulting poor idle quality]. Can't be sure of the problem, but there is something not right there.
Le Mans Master
Joined: Dec 2007
Posts: 6,422
Likes: 591
From: McHenry Illinois
Check to make sure the fast idle cam is not holding it off the idle screw. It's on the right side of the carb and there is a fast idle adjusting screw on the same side under the choke mechanism. Also make sure the choke is all the way open when it's warmed up.
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Thread Starter
Racer
Joined: Apr 2006
Posts: 340
Likes: 0
From: Warrensburg MO
I did check the fast idle, which it does clear, and the choke goes fully open. I was wondering also if the primaries are open further than they should be causing the situation. I don't recall there being any screw adjustments for them like the Holley. The only thing I really see is the linkage between the primary and secondary on the left side of the carb. Guess I need to do more studying on operation of the Q. Thanks
TommyJ
TommyJ
