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Damn Quadrajet!

San Diego 69350

New member
Joined
Jun 26, 2007
Messages
2
Location
San Diego CA
Corvette
1969 LeMans Blue 350/350
I hear these things are good when you get them right. How do you get them right?

My car is a 69 350-350 all original. I currently have the two front screws opened at 3.5 turns. Theses are the air idle adjustments. Car doesn't smell rich. Is this a good starting point? I'm in San Diego about 4-5 miles from the coast. The air is pretty dry here.

Here's my biggest problem. The car can idle perfectly at 800-850 until I drive it. After driving, when I come to a stop the idle stays up at around 15- 1800. It sometimes comes back down slowly and other times doesn't come down at all.
The choke is working fine and isn't the cause.

I had soma vacuum leaks in the intake manifold gasket and the carb to manifold gasket. Replaced both and eliminated the leaks.

Any suggestions are apreciated.
 
Joined
Jan 1, 2002
Messages
7,246
Location
Washington, Michigan
Corvette
'67 Marina Blue Convertible
My car is a 69 350-350 all original. I currently have the two front screws opened at 3.5 turns. Theses are the air idle adjustments. Car doesn't smell rich. Is this a good starting point?

Don't go by "turns" - the idle mixture screws are adjusted using a vacuum gauge connected to a full manifold vacuum source, and adjusting the screws to obtain highest steady vacuum reading.

Make sure your fast idle cam is moving freely, and drops out of the way of the idle speed screw when it's warmed up; sounds like it's sticking.

:beer
 

Vettehead Mikey

Well-known member
Joined
Aug 26, 2003
Messages
3,486
Location
Not that far from Ottawa
Corvette
1973 Coupe
It sounds like your primary shaft is sticking partially open. This is very common on high mileage Qjets and is caused by the throttle return spring constantly 'pulling backwards' on the shaft via the bellcrank.

The hole in the carb baseplate wears into an oval, and causes the shaft to hang partially open as well as causing an air leak.

Next time it does it, just barely tap the gas pedal. If it settles back to normal idle, bingo. Works even better if you do it with the hood open and your hand on the linkage.

Lots of carb shops can fix this by installing a bushing in the baseplate.
 

Bill75

Well-known member
Joined
Jan 1, 2004
Messages
698
Location
Somers CT
Corvette
75 Coupe ZZ4, Brodix IK-180's, Headers,TK0-500
It sounds like your primary shaft is sticking partially open. This is very common on high mileage Qjets and is caused by the throttle return spring constantly 'pulling backwards' on the shaft via the bellcrank.

The hole in the carb baseplate wears into an oval, and causes the shaft to hang partially open as well as causing an air leak.

Next time it does it, just barely tap the gas pedal. If it settles back to normal idle, bingo. Works even better if you do it with the hood open and your hand on the linkage.

Lots of carb shops can fix this by installing a bushing in the baseplate.

Here's a source for a repair kit to install new bushings yourself if you choose to do so.

http://www.cliffshighperformance.com/parts.html
 

San Diego 69350

New member
Joined
Jun 26, 2007
Messages
2
Location
San Diego CA
Corvette
1969 LeMans Blue 350/350
Thanks guys for the responses. I haven't tried the light tap only a more aggressive tap (like kicking down the choke).

Here's another thing it does. When I drive it and come to a stop the idle will go up and fluctuate up and down between 15 - 2100 rpm's. That makes me think it's not a "sticking" issue?

I'll keep you updated. Thanks again
 

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