I had my V6 rebuilt as a long block and I put it back together. Not my profession. It now has the classic backfire and popping. I had an old car shop do some other work and they decided it likely is out of time on the rebuild. It does run when the timing is very advanced, the timing mark is almost straight up but dies when bringing it towards the timing marks. I am pretty sure the carbs ok, and it has an HEI on it. It is also running very rich. Looking for opinions before I tear into the timing cover.