Originally Posted by Timmy-Boy
I have a 1972 buick skylark with a 350 and a 2bbl carb. It is smoking black out of the exhaust. It is not excessive or anything and it smells like fuel. Ive checked for every sign of blown head gaskets i can think of. Its not burning oil and its not burning radiator fluid. It does have a problem when you give it to much throttle throttle to quick it bogs. It probably doesnt help that the spark plugs are pretty old. Im thinking it needs the air fuel mixture adjusted.
Check that the air filter isn't dirty and if using the stock filter housing, check that the snorkel air inlet isn't housing a mud dauber nest or something!
Check the choke: remove the air cleaner lid after the engine is warmed up fully. The choke should now be wide open. If you warm the engine w/o driving the car, the throttle has to be opened slightly to allow it to pop open in some cases. If it doesn't fully open the engine will run rich, w/black smelly smoke.
There's also a chance the air bleeds (red arrows, below) have become clogged. You can use a can of carb spray. Follow the directions and see if that helps- sometimes that's all that's needed.
Lastly, readjust the idle mixture screws. IIRC, I used to use 2 turns out from lightly seated as the base setting. Start and warm up the engine FULLY. If it doesn't want to idle, give the screws an additional 1/2 turn each until it will idle steadily. Then adjust the idle mixture screws to give the best vacuum or highest idle speed. You may need to readjust the curb idle to bring the speed down if they were out of adjustment.
If it's none of the above, time to rebuild it. I would strongly recommend you buy a new float when you get the rebuild kit.
Rochester 2G carb air bleeds