Quadrajet Problem Solving > Diagnose a Quadrajet carburetor problem
weird vacuum leak
Marx3:
I never checked the baseplate for warpage, cause the carb ran perfectly without leaks before I re-calibrated it.
I'll check up on it though.
Good idea with the machinst dye. I have some of that stuff in blue.
sticking power valve? The spring is stock. everything is stock, besides the jet and rods.
Ethan1:
--- Quote from: Hillbillyenginering on May 26, 2016, 09:42:04 AM ---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.
--- End quote ---
I like your thinking! 8)
Definitely worth a shot.
Hillbillyenginering:
You said that normal driving you never have a prob!em. After WOT it has an idle issue.
Prior to WOT,the power valve is usually down from vacume. Wot takes away vacume. Hence spring pushes the valve all the way up. If it sticks, vacume will not be able to seat it. Causing more fuel to enter the idle circuit.
If it was just a vacume leak, you should see a lean ssue on four cylinders, not two. Also it should have higher rpms.
But maybe you are having a primary or secondary ignition issue.??
I know it seems odd. But I fought a carburation issue for years. Even swapped manifolds on my toro.
Finally the old Mallory coil took a dump. Changed coils and carb issue went away. But of course I bought a MSD distributor first.
Hillbillyenginering:
Just throwing this out there.
Havew you used a timing light when it is tuning rough, after WOT. And see is one of your weights are sticking. Causing way too much advance at idle?
Marx3:
I am not sure the idle circuit gets more fuel when the needles are raised... I mean, that not how it works?
Ill check up on the movement of the powerpiston.
The carb is completely rebuild and is in overall good shape.
It IS a vacuum leak. Idle quality can clearly be affected, when spraying break cleaner at a certain area between the manifold and the baseplate.
Timing has been under suspicion. It is rock steady in idle and the distributor, like the carb and the rest of the car, is in good condition.
It seems the problem only starts after a WOT situation.
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