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Carb gasket confusion (sbc)

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1991 305 converted to Quadrajet carb with a summit intake and stock reman Quadrajet for a 1983 k20 (the vehicle that it is in)

I’m going to preface this by: I have it “fixed” and running well now, but ….

ran fine when parked a couple months ago. Went to use it and it was stumbling and stalling and running very poor altogether. Limped it through the project (it’s a yard truck) and kept it running by cranking up the warm idle.

fast forward to tonight: started it up and was still running poor. Let it warm up and settle into its warm idle. Checked it with brake cleaner and the carburetor gasket was leaking.

so in an attempt to not break anything I put my torque wrench to it and started tightening. Finally got the bolts to tighten at 20 lb-ft. Probably too much but they were already more than 15 by hand. So I kept working them down compressing the gasket. (Stock thick paper gasket with internal stops).

so as I was doing this I kept checking for leaks. Still leaking. Finally got the bolts to stop turning at 20 lb-ft and still leaking. So i reved the engine some for about 20 seconds and the idle came up and stayed up. Reved it again for about 20 seconds and the idle came up again and stayed up. Rinse and repeat a couple more times until it seemed steady. Checked the gasket for leaks and no leaks. Lowered the hot idle and checked again, no leaks. Purrs like a kitten.

so: why was it leaking and then only stopped leaking after racing the engine? Made no other changes between leaking and no leaks. Just raced the engine for about 20 seconds or so.

also: can someone recommend a better carburetor gasket? I’ve lost confidence in this one. It was replaced last fall and Only has one or two snow storms on it before giving up. Really can’t be dealing with that when it’s -20f out.

And: how tight should the bolts be. I’m sure they are over tight, but that is what it took to get it to seal. Again, this is a fresh reman carb and a new manifold when i put the motor together.

thanks in advance
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· Registered
16,303 Posts
If that was a Holley at 20 ft pounds the mounting ears would have bent and you‘d be in trouble.

With a Q-Jet you probably got away with it but not something I‘d recommend.

Some gasket materials dry out without regular use. Probably the shortest fix would be to sandwich the positive stop gasket with a simple single layer gasket on each side.

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