It is a 1976 Chevy Silverado. Gas. 5.0 L. What could cause black soot to come out of the exhaust? I’ve noticed a HUGE loss in power and stalls on me occasionally. I bought the truck a month ago. I had carb problems the first week. Found little pieces of dirt in the carburetor so I cleaned it and put it back on.

  • Welcome to the site. Can you please edit your post to include more information about the truck? Knowing the year, and which engine is installed will help you get a specific answer. – CharlieRB Feb 1 '18 at 16:59

Too much fuel. This happens to diesel and is somewhat normal (for your year, anyway, not so much anymore) with small amounts of soot. But for gas engines, there should never be black soot*.

This would also cause stalling.

*Ok, sometimes carbon deposits are loosened when you floor a car that's never been floored before but besides that...

  • it also backfires and when that happens a mist of gas comes out the top of the carb I tried tuning the carburetor nothing changed. I found the choke was completely closed on a cold start I held that open and still no change. – Isaac Feb 1 '18 at 22:02

If it has done that since you got it, it's probably tuned far too rich.
That means that it gets too much fuel. The excess of fuel does not combust completely, resulting in a lot of sooth, higher than normal concentrations of the lethally dangerous gas carbon dioxide, a fuel smell from the exhaust, and your catalytic converter will burn up if you have one. There is a certain sweet spot regarding fuel amount. If it's less or more than that, the engine will make less power and the car will drive terribly.

If it is a problem that has developed recently, it can be a multitude of things. If it's a carburated engine;

-tuning got messed up somehow
-choke can be stuck closed(partially)
-fuel level in float bowl may be too high,
-too strong fuel pumps may force excess fuel into the carb
-hell, even your needle could be broken.

If it's an injected engine;
-MAP, MAF, IAT or any other sensor may be broken and reporting wrong values
-fuel pressure regulator may be broken

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