1962 rpm increases when air cleaner goes on?

[aa010175]

I have a stock 390 motor in my 1962 Thunderbird. I rebuilt the Stock autolite, 4100 carburetor and now it won’t idle at anything under 750 RPMs. It just quits after that and when you do have it running and you put the air cleaner on the RPMs increase considerably. What would cause an increase in RPMs by putting on the air cleaner stock? thanks, Dave.

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[Tom Alpers]

Did you take apart or adjust the linkage for the secondaries? Maybe they are not closing all the way. What about the air cleaner hitting some of the linkage?

 

[74 Harley]

You could also have a vacuum leak.

 

[bmac1060]

Sounds like a large vacuum leak. Plug up ALL ports from the carburetor and intake manifold to see if this fixes the problem. If so, reconnect one at a time to identify what the culprit is.
It is also possible the carburetor base gasket is not sealing properly.

 

[Nakusp]

I agree that vacuum leaks are likely the problem. I prefer the Holley carbs over the Autolite 4100.

 

[Bruce Hardy]

I would double check the carb install. It might be tight but crooked on the intake. Or you could try drizzling gas around the gasket and see if there's a responce.

 

[aa010175]

I put on a new rebuild 4100 and it runs good now. Thanks