Classic car question, '63 Falcon loses acceleration when the engine gets hot

Question

The car runs fine when I leave work, I drive for about 30 minutes. I stop at the store, I get back in the car and start her up.

When I press on the gas, she barely has any acceleration. I have to stick the pedal all the way to the floor and then she moves slowly. Very sluggish. It's almost like the compression is gone.

Any ideas what might be causing this?

Answer 1

Here's my theory, just because nobody else seems to have thought of it.

I don't know about '63 falcons, but on most carbureted cars, there's a large gate in the air intake path that pulls air from a riser on the exhaust manifold. The idea being that when your engine is cold, the hot air off the manifold will improve driveability and help your engine get to operating temp quickly. Once it's there, a temperature sensor lets vacuum through to a diaphragm which moves the valve to suck in normal, unheated air.

It's normally a good idea. However, all the systems i've encountered tend to fail in the hot-air-off-the-manifold position. And when the engine is hot, breathing superheated air of course gives terrible power output and make the engine feel sluggish, like you describe.

So that's my theory. Try to find if your car has this feature - look for a tube coming off the manifold and going to underneath the air cleaner. Then if it has it, try bypassing it by propping the air valve open to see if it's your problem. Good luck, whatever it turns out to be.

Answer 2

the fuel pump may be breaking down on it ,sometimes on those when the pump would get hot the diaphragm in the pump would cause this too happen,you might want to check that just to be sure,good luck.

Answer 3

heat causes metal to expand. if your rings are worn this will cause you to lose compression after it heats up. do a compression test after your engine is warmed up.