I have a 78 Z28 350 with Quadrajet. Took to paint shop running fine. It was there two months. It looks good. But now barely runs. Running way rich even when choke is off. I put a kit in the carb but made no difference. The car ran perfect before going to the shop. When we fired it up after rebuild it ran great for a few seconds on the prime gas then ran bad and wont hardly idle. Blows black smoke and smells bad of fuel exhaust. Any other ideas. Carb kit did not help. Bad gas maybe. Let me know your thoughts.