Quadrajet Problem Solving > Diagnose a Quadrajet carburetor problem
weird vacuum leak
Hillbillyenginering:
A couple of question.
What year is the intake manifold?
How did you verify the vacume leak is there?
Does the manifold have the internal heat tubes in it like some of the Buicks did?
Marx3:
the car / engine is from 1976 and completely stock.
I have been wondering if the intake is uneven or something, but this problem has never been there before. The carb was rebuild previously. never any problems. Then I took it off to recalibrate the idle and primary systems. then the problem started. Originally I overdid the idle calibration( too much fuel and alot of bypass ), which made it impossible to get the idle below 800 rpm. otherwise the car pulled like a freighttrain with the new, more generous jetting.
got the calibration down to stock again. now I encountered this problem. smooth idle at 5-600 rpm right untill the car has been driven at wot. Then the idle goes bad and climbs a bit.
I veryfied the vacumm leak by spraying brake cleaner around the baseplate, very carefully. Right around the front passenger side bolt, the idle is clearly affected, when psrayed with brake cleaner.
No these late 500 engines did not have the Buick-type heat passage.
Hillbillyenginering:
I don't want to sounbd like D BAG.
But did you check the base for warpage?
I might try purissian blue on it and bolt it down and see if it is contacting correctly.
Thick grease will work also.
Maybe it is two problems.
Vacume leak and sticking power valve or too strong of a spring.????
Ethan1:
--- Quote from: Hillbillyenginering on May 25, 2016, 08:06:54 PM ---I don't want to sounbd like D BAG.
But did you check the base for warpage?
I might try purissian blue on it and bolt it down and see if it is contacting correctly.
Thick grease will work also.
Maybe it is two problems.
Vacume leak and sticking power valve or too strong of a spring.????
--- End quote ---
I agree. Check for warpage. Use some machinist dye and see if it contacting everywhere correctly. Also, use a straight edge as well.
Hillbillyenginering:
Something else that you can try.
Get some liquid machinests dye, dykum. Or that liquid from bingo robbers.
Put it in a small syringe, when you have verified it is having the vacume leak, squirt a little on the area. When you see it get sucked in, shut the engine off. Let sit for 10\ 15 minutes to let it dry. Remove and it should show the path.
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