Gray smoke when warm

[John Milner]

I am working on a 400 engine and it seems to want to smoke gray smoke when fully warmed up. The compression is around 9.75:1 with a 224/230 hydraulic cam. The carburetor is a 1407 750 Edelbrock. It fires right up and idles great when cold. There is no smoke when cold. The engine is very responsive when cold with no flat spots. Once warm, the engine still idles good. However, there is a flat spot right off idle when accelerating. It seems to clear up after the stumble. On warm idle, there is gray smoke coming out of the exhaust. I’m wondering if the 1407 750 Edelbrock might a a little rich for the engine?

 

[WileERobby]

Perhaps a closer look at the smoke ? Is there a hint of either a whitish, bluish, or blackish tint in the smoke ? Depending on any, it could be coolant, oil, or fuel condition as a cause.

 

[John Milner]

It’s really tough to say, but maybe a little bit of a black tint? The engine doesn’t seem to use any coolant or oil.

 

[Fran Blacker]

Losing coolant or smell of anti-freeze.

 

[khryslerkid]

Pull you plugs for a look. Keep track of where each plug goes and look for any differences.

 

[1STMP]

Smoking after warmup is
usually an indication of
worn valve stem seals
or quides.
White smoke=coolant
Blue/Grey smoke=oil
Black smoke=fuel
(As a general rule)

@khryslerkid is correct
that your plugs will tell
the story.

 

[Geoff 2]

I doubt the smoke is related to engine tune. Smoke comes from engine wear.
The 400 engine has the highest rod/stroke ratio of ALL the popular BB engines. What that means is that it does NOT like cam duration at low rpms [ see below ] when you are taking off.
And the carb is not the problem either, although it may need fine tuning.

The fix is a LOT of timing at idle. Do this simple test: start engine, then turn dist to increase timing to about 30* [ not critical ]. Readjust carb idle & mixture screws. Take for short test drive to check on hesitation. I am betting it will gone.....or much reduced.

Report back.

 

[John Milner]

Thanks for the replies everyone.