ok guys, here's the deal. i have a 1985 GMC jimmy with a 305 in it. well yesteday on my way to work it stalled on me and i found that i wasn't getting any spark. i found the problem to be the magnetic pickup in the dizzy, so i pulled the dizzy and rebuilt the whole thing (i got bored at work, and since we had all the parts in stock...) any way. before i pulled the dizzy i marked the rotor location and the base location after i pulled around to TDC like you should do. so i put it all in and it lined up perfect with my marks. well at first crank it ran alittle rough, but since we only work on new vehicles at the hummer dealership, no one had a timing light. it felt fine at work atleast fine enough to get it to my house, i'd rev the motor and it seemed alright, well i pulled it out the shop and put it in drive, i stomped on it and i got a backfire through the carb, so i got home after it was backfiring all the way home, and i looked for a timing mark on the timing cover, THERE'S NO TIMING MARK?!?!?! i guess the PO decided he didn't need it so he took it off. well i decided i'd time it by ear, everything i do i still get a backfire through the carb... so heres the problem summed up. i'm getting a backfire through the carb when the engine is under a load only. what should i do to fix the problem???