I recently got the '83 Z28 running after 9 years of sitting. It was running fine other than a slightly rough idle and suddenly after changing the spark plugs, to pre-gaped plugs, the car ran fine. It hadn't been driven around because of a broken/hanging transmission mount, but suddenly after removing the AC pump (no belt was previously attached) the car wouldn't run. It started popping really deep, and smoke poofed out of the headers. After trying a couple of times, the car started to backfire (smoke and sometimes flames) out of the carbs. Is this a timing issue? Is a valve stuck open? Fuel problem (9year old fuel)?? How can I fix this