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Discussion Starter · #1 ·
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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Discussion Starter · #5 ·
Where can I find the tan gasket? What is it called so I know what to ask for?

i can try to check to see if it is warped. It may well be. When I first put the engine together, I just had a single layer paper gasket. Over a period of time it started to leak as well (could hear it howling as it was sucking past the gasket). It took quite a bit is torque on the front bolts to get it to seal up that time as well. But it did stay sealed until I pulled the carburetor to find different leak (deteriorated vacuum cap).

tired of vacuum leaks….
 

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Discussion Starter · #10 ·
Thank you for the reply. I’m hoping I didn’t warp the base too badly by cranking down on it.
They had the thick felpro gasket like what I had, but kind of didn’t want the same one since it failed so quickly.
The fact that the cometic was half the price didn’t hurt anything either.

the last time I had a 4-hole gasket like this one I trimmed it out to match the manifold (dual plane). Is there any need or advantage to opening it up? I was just afraid of the gasket getting weak over time and collapsing into The intake. Any need to worry about this?
 

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Discussion Starter · #13 ·
Just a quick update. I got it fixed. I installed the cometic gasket as it was and did not use any sealer because I didn’t have any.

i should have posted a picture of the old gasket and maybe I still will, but I couldn’t find anywhere that it might have been leaking. There were good imprints all the way around on both sides and I couldn’t see anywhere that it was blown out, particularly on the backside where it was leaking.
I have a feeling it was leaking at the vacuum port at the back of the carburetor. When I pulled the hardline fitting for the booster the adapter didn’t feel particularly tight and the Teflon tape looked to be pretty ragged. I replaced the tape with paste and installed new gasket with the carburetor torqued down to 10 lb-ft as recommend above.

The issue appears to be resolved and it runs like a champ again.

do I need to worry about the 4-hole gasket hanging loose over the open plenum? It’s an open dual plane plenum under the 4-hole gasket which leaves a lot of gasket unsupported. Is this a concern?
 

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Discussion Starter · #15 ·
Thanks for the reply. You’ve described exactly what I was wondering. I know I can trim the gasket, but do I need to?

the last paper gasket I used I trimmed it to the plenum walls. This gasket is quite a bit thicker though, maybe 1/8” thick. If it needs to be trimmed, I’ll pull it this spring and do it. But if it’s fine leaving it, I’m not looking for a reason to work on jt. But I dont want to lunch the motor by trying to feed it a carburetor gasket either.
 
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