when i fire it up after its been sitting for a while it runs like its running on like 4 or 6 cylinders...VERY ROUGH....and i have to give it a good amount of gas to keep it running....(carbureted)....today it was back firing and black smoke was coming out of the exhaust......i just replaced the spark plugs (ac delco rapidfire)about a month ago....but i know im past due for an oil change.....

could the oil b the problem or does it sound like someting else?
cuz i think i may have 10w-40 in there and i heard that if the oil is too thick it may run crappy.....

 

It's not your oil.

Sounds like maybe the choke pull-off isn't working properly. It's the little vacuum canister on the pass. side front of the carb. It's job is to pop the choke plate slightly open (1/8" or so) against the choke spring as soon as the engine starts up. This keeps from flooding the engine with a fully-closed choke plate.

When you fire up the engine the arm on the canister should go from fully extended to fully retracted and remain so. Make sure it is. Also, give a little pull on it with your fingers. It should take quite a bit of pulling to extend it against the vacuum canister. If it pulls out real easy or never fully retracts in the first place- it's shot. It's available from your local auto parts store.

 

you are talking about the actual flap for the choke right...cuz if so...thats not it...cuz i thought that may have been it so i started it up and had the air cleaner off and the choke didnt stay shut....it opened after a while...

 

It needs to open slightly IMMEDIATELY after strtup. That's the job of the vacuum break. The choke will open up on it's own in a few minutes of running, but the initial pop open comes from the vacuum break.

 

yah sorry thats what i meant......im almost positive that my choke isnt the problem.....i was reading another post and i think it might b the charcoal canister....cuz this other guy was having the same problems as mine....

would you think that could do it?

thanks for the help

 

If it's "purging" when the engine is cold it will over-richen the mixture and it can run bad. Easy to test- unplug the purge line from the charcoal canister and see if the problem persists. If not, that's it. If so, that's not it.

The purge line is the one that eventually T's into the PCV line near the carb.

 

MattW, where is that other post about the charcoal canister? I'm interested to read about that.

My car behaves like yours, and I'm getting a gasoline smell at times. Doesn't backfire, but runs on sometimes when I shut the engine off.