305 Timing issues
 

I have a 1979 K5 with a 1986 305. I changed the timing set because the original was badly worn. Edelbrock Performer EPS intake and 1406 carb. The engine runs great at idle, but when I go to time it the mark on the distributor is off to the side at around 10 degrees ATDC. I retard the timing to where it should be, 10 degrees BTDC, and the engine won't hardly run and it diesels really bad when I shut it off. There is also no power. The harmonic balancer is good because I checked it after I changed the timing set. Any help is greatly appreciated guys. Thanks.

First am I to take it you replaced timming chain, cam/crank gear? If so, what position where the timming marks? Dieseling at shutoff usually is too far advanced timming. Are you on #1 cylinder with timming light? What rpm are you checking timming? What is the distributor mark you are talking about?

I replaced the whole timing set. The timing set was replaced correctly. I'm not too worried about that. The marks were at 12 and 6. I'm timed to #1 cylinder. It's dieseling because I have it retarded so much to get it back to as close to zero as I can get it. Sorry about the timing mark comment. I meant the slot in the harmonic balancer is 10 degrees clockwise or ATDC. I was thinking the problem was in the distributor, but I replaced it with a new one and have the exact same problem. I can't even dial it back to zero. The closest I can get, without it dieing, it around 3 or 4 degrees ATDC. I'm suspecting that I have a bad timing light. I'm going to buy a new one and see if that's my problem. Thanks for the help.