Ok, for some reason My car started backfiring under load. It ran perfectly before I went to work. Came home 20 days later and it has an issue. The car backfires out the carb bad when I give it more than a quarter of a throttle. Initially I thought this was timing so I checked it. It's set and 5 degrees advance. So I ruled that out. Could it be something with the carb? Like the power valve or something. Carb is a holley 670 street avenger, car is a 94 l69 305 with a B&M 144. I thought it may have been the S/C to base gasket replaced it. Same thing happening still. Could a loose ground cause this problem maybe?