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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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A carburetor does not need any more then about 6 pounds of torque or basically just a little bit hand tight once the bolt starts to get tight. About a 1/4 of a turn or a hair more past when getting tight will do. Also you want to use a thick enough gasket to help seal things. I use gaskets that are at least an 1/8 inch thick.

Many factory ones that come in rebuild kits at least for Qjets depending on where you get them from and also using stock type gaskets they are so thin they will almost always leak. I don't think they are even 1/16th of an inch thick.

You might want to check your carb base plate bottom or your intake both and see if they are flat with a straight edge if you can get access to one.

You are lucky if you have not broken the ears of the corner of the base plate on those as on Holley carbs they would most likely have broke.
 

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Glad to hear it worked out for you. As far as the gasket part goes that hangs in the open you can just cut the material that hangs into the open. When I use a 4 hole gaskets on my dual plane I just cut the two in between pieces on each side making it a big elongated shape but still seal in the middle part to keep both sides sealed. Since yours is open just cut what you need off and leave enough to cover the square radius of the intake. Basically leave enough material to cover the whole area of the intake and the rest that hangs over won't make any difference since it will have no purpose just sitting there on top of nothing pressing up against it.

Basically like an open gasket that is used on Holley carbs
 
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