Vapor Lock?

[Charlie F.]

My 1966 327/300 4spd...after highway travel of 1 hour approximately the motor stalled when I pulled in for fuel. It caughed, sputtered and chugged until it finally caught. An hour later it stalled when I pulled off the highway. I'm "told" the fuel line and maybe the carb (new Holley) overheated...that the fuel actually vaporized. After sitting for 30 minutes I was able to drive home. Any ideas about causes and...remedies? Thanks. this is my first visit to your forum.

[Joe L.]

Re: Vapor Lock?

My 1966 327/300 4spd...after highway travel of 1 hour approximately the motor stalled when I pulled in for fuel. It caughed, sputtered and chugged until it finally caught. An hour later it stalled when I pulled off the highway. I'm "told" the fuel line and maybe the carb (new Holley) overheated...that the fuel actually vaporized. After sitting for 30 minutes I was able to drive home. Any ideas about causes and...remedies? Thanks. this is my first visit to your forum.

Charlie------


The very first thing I would do is to inactivate the carb heat slot in the intake manifold. To do this you need to remove the carburetor. On the manifold carb flange you will note a wide slot that exists just forward of the primary bores. At each end of slot is a hole. You need to plug these holes. Doing this will eliminate exhaust gas from passing through the slot and heating the carburetor.

With the manifold on the engine, your best bet to plug the holes is to obtain soft plugs of the appropriate size from a good auto supply store. These look like miniature freeze plugs. First, clean the holes of as much carbon as possible with a small, round wire brush. Then, drive these plugs into the holes using a driver punch that just fits into the cup of the plug. With the manifold off the engine, you could tap these holes for allen head NPT pipe plugs.

Reinstall the carburetor using a new gasket. Install the gasket first, then install the stainless steel shim baffle plate, and finally install the carburetor. Done.

By the way, if you note when you remove the carburetor that there is no stainless steel baffle installed, that could be the whole cause of your problems. Without the baffle in place, the exhaust heat will come in direct contact with the carburetor, causing it to get excessively hot. In many cases, this will actually destroy the carburetor. With the heat slot plugged as described above, you don't really need the stainless steel baffle, but I would install it anyway.

GM abandoned this carb heat slot after the 1969 model year. They should have abandoned it when it was first conceived.

[John H.]

Re: Vapor Lock?

Charlie -

Photo below shows the "hot-slot" with 7/16" cup plugs in the end holes as Joe noted.

[Domenic T.]

Re: Vapor Lock?

Also check the heat riser and see if it's stuck closed.
Plugging those holes makes sence.

DOM