[joeinbcs]

Hi All,
I've been a away for much of the Summer, and my car has been with an upholstery guy. It had been producing black smoke on start up, but seems to have gotten dramatically worse, and now runs poorly.
I took the air cleaner off and saw that the area beneath the intake manifold had a coat of sooty residue, and that sooty smoke escapes from somewhere under the manifold when I rev the engine.
Any ideas what is causing this?
I'm going to take it to my mechanic, but don't like to appear as clueless as I actually am when I discuss with him!
Thanks, Joe

By the way, its a 401, single 4 barrel

[MartyWorld]

The exhaust crossover located on the underside of the intake manifold is probably leaking at the core plug. Remove the intake and install a new core plug.


Marty

[CTX-SLPR]

If the valley pan has been replaced there might not be seals on the bolts. Mine does that.

[kaycee]

I had this happen on a 425. It was the core plug on the underside of the intake manifold. I forget the actual size but it was 2-2/12 inches, and any parts store that has Dorman products should fix you up.
kaycee

[kaycee]

Another thing to check if you pull the carburetor off too (which I would suggest) is the metal gasket and regular gasket between the carb. and intake manifold. These won't cause the 'soot' problem under the intake manifold, but will affect running especially on warmup, and at the same time you can clean the 'groove' on the top of the intake manifold that conducts exhaust heat to warm up the carb., and with the intake manifold off also clean the exhaust ports in the manifold and heads.
kaycee

[joeinbcs]

Thanks, fellas...it turned out to be the core plug on the underside of the manifold...had a large hole in it. I was having the carb rebuilt anyway, so glad to get to the bottom of this now. Joe