When i got my car about 8 months ago it ran great, it hasnt been street legal yet so i mostly just take down to the corner and back ,or let it idle while i work on it, lately it has been running very rough like its running very rich, it has even stalled a few times. I took the air filter off and and it seemed to fix it. The car was sitting for a while before i bought it, and it had a full tank of gas, now its almost on empty, so im wondering if its the crud in the gas tank thats making it run rough?