I have a 91 Chevy short school bus 8 cyl gas it has been sitting for over a year I put in a new battery & it started right up ran a few minutes produced black smoke from the tail pipe then died. It wouldn't turn over again until half hour later. I took a chance & took it for a ride around the block came back and it shut down again. All levels were OK Finally I got it started. Can it be the gas ? should I spray the carb with carb cleaner? Open to any suggestions?