Re: 1947 Super Clipper idle problem

Posted by Tim Cole On 2012/2/3 21:09:17

Dear Packard1949:

The technical term for your problem is called a "coast down stall". In computer controlled engines these are usually confined to problems at the air intake. That should provide a few clues.

My guess is that you have dirt in the idle circuit of your carburetor. This is supported by the motor running worse when you remove the air cleaner. I would try racing the motor and momentarily placing your hand over the carburetor. The suction will help disldoge any dirt in the air bleeds. If the car runs better then you have a dirt problem. Air leaks can also cause a coast down stall, which may be rememdied by careful tightening of the screws that hold the base to the float bowl section.

Whomever sold you the Mighty-Vac made a good recommendation as the unit is fine for checking motor vacuum. Your idle vacuum should be between 17-21 inhg. Your readings of 11-14 are low so I would do a compression test. If the static compression is good (100 or higher) then your timing chain may be worn or you may have a vacuum leak. Usually those readings due to vacuum leaks would also have significant driveability problems.

I have a really sensitive vacuum gauge that I store in a foam lined box, I don't use it except when I need to look at mechanical problems like weak valve springs, broken rings, low cylinders, and faulty ignition.

There is another possibility and that is a problem with the overdrive relay. When these relays get old the ignition interruptor sticks and kills the motor. This is that extra wire on points side of the coil. It can be disconnected and the overdrive will still work.