Black Smoke Near Head

[RichardR]

Hi,
I tried a search but things seemed confusing. I have a 1971 Plymouth Scamp with the 225 slant 6. It starts great. It can sit for 2 weeks and still start great. It does idle a bit rich though. When the car starts there is no smoke under hood. Once you rev it, you can see a puff of black smoke come out roughly where the choke pull off linkage goes to the manifold. Back to idle no problem. Rev it quickly again, you get the puff. Could it be a intake/exhaust gasket with a hole?

 

[Badvert65]

If it is an exhaust leak, you should be able to hear it, but my first guess would be a leaking gasket.

 

[slantsixdan]

The '70-'72 Slant-6 exhaust manifold has an open hole where the choke thermostat goes (not the "pull off", which is up on the carburetor itself). In that hole sits a stainless steel cup, and on top of that cup sits the choke thermostat. There's a gasket between the cup and the exhaust manifold. If you are seeing smoke, that's probably where it's coming from. The gasket is no longer available; you will have to make or find one (I think I have one left; send me a PM if you want it).

There should not be any smoke, though. Carburetor operation and repair manuals and links to training movies and carb repair/modification threads are posted here for free download.

 

[RichardR]

The '70-'72 Slant-6 exhaust manifold has an open hole where the choke thermostat goes (not the "pull off", which is up on the carburetor itself). In that hole sits a stainless steel cup, and on top of that cup sits the choke thermostat. There's a gasket between the cup and the exhaust manifold. If you are seeing smoke, that's probably where it's coming from. The gasket is no longer available; you will have to make or find one (I think I have one left; send me a PM if you want it).

There should not be any smoke, though. Carburetor operation and repair manuals and links to training movies and carb repair/modification threads are posted here for free download.

ya, that's what I meant. The thermostat area. If it's just an gasket that's not too bad. And what sort of sound? Like the roar of the motor as if it had no exhaust?

 

[slantsixdan]

Depends how big the leak is. That gasket would have to be pretty much completely blown out and gone to make it really roar; a break/gap in the gasket would make a loud spitting/tapping sound that would increase in frequency with the engine speed.

 

[RichardR]

Depends how big the leak is. That gasket would have to be pretty much completely blown out and gone to make it really roar; a break/gap in the gasket would make a loud spitting/tapping sound that would increase in frequency with the engine speed.

Right. Ok, thanks for the info. The choke thermostat gasket looks homemade as I look at it now in car installed