So I just got my new 383 running recently and thought I had a good handle on the tune but then today I was driving home and it started to idle rough. A little smoke started to come out the tailpipes (rich black not oil blue). So then I get it home with no other real symptoms and let it cool so I can check things out.

So I went out and started it and it seemed to idle a little high but smooth after getting cool so I could touch the motor. So I started by trying to reset the idle mixture with the screws and discovered I could seat both of them and the motor seemed to run fine!!! I have no idea what to look for but I suspect there is some sort of fuel leak that is keeping the thing running.

Help!
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Oh sorry this is not my car motor its a Q-jet 383 with no computers at all.

 

Can we assume this is not a computer q-jet, and that the distributor isn't either?

 

Yes -- no computer controls.

I did have a problem when I was first running the motor that the long bolts holding the carb down bottomed in their holes in the intake just before contacting the carb air horn. I didnt figure out it was leaking until the carb gasket started screaming like a blade of grass between your thumbs.

I took some more washers and I thought I solved that problem but I suppose I could have an air leak there -- I guess Ill swing by pep girls and grab another gasket just in case.

I still cant see how a vacuum leak would allow the engine to run with the mixture screws seated though. I guess I have gas coming out of one of the primary or secondary feeders and I have a stuck open needle.

 

The best thing to use to hold down your carb is studs.This will stop any vacuum leaks you have at the base of the carb. Did you go out and see if you are getting wet in the primaries or secondaries. these quad are known to be famous for flooding after a fuel filter change especially. I never worked on any 4 barrel quad carbs. I always run holley, easy to work on .The idle mixture screw is used to do what it says. On most carbs it is in to lean and out to rich. If yours goes all the way in it seems it is getting fuel from another source.

 

Ill let you know after work today -- should be home around 6. Then Ill look at it again.

 

It takes some pretty long studs to go through the front of a q-jet.

The bolts are sized assuming the 1/4" thick gasket is used. If you're going to the parts store, try to get one of those. Then you don't have to use washers stacked under the bolt head.

A proper seal between the intake and carb is the first step to getting the car to run right. Until that is assured, don't go messing with anything else.

 

OK.

And I didnt think I could use that thick 1/4" inch gasket?? I have always used the thin one from Mr. Gasket that is like 5 sheets of paper thick. It seemed to me that that thin gasket sealed some passages in the throttle plate of the carb that the thick gasket looked like it would leave open.

I have 2 of the thick ones laying around so That would be nice if I could just use those.

 

The thick gasket works for all Chevy q-jets that I'm aware of except the very early ones with the exhaust cross-over passage built into it.

 

Sweet.

 

Ok I got to it today.

Put the thick gasket on and blew into the fuel inlet housing with air a little.

Seems to be running fine now.

Thanks for the help although I never really "found" anything, the thick gasket saved me a trip to the parts store.