i can think of several things that will cause this condition, cracked dist. cap, crossed or bad plug wires, bad timing chain. i'm trying to reset my timing after replacing an intake and i can't seem to get the initial set due to it backfiring through the carb. i know i'm on TDC and the rotor is pointing to the number 1 plug position on the cap. i've plugged the vacuum line any obvious stuff i've missed? i plan on replacing the rotor and maybe the cap on this 454 w/hei.
thanks for any suggestions.

You could still be 180 off. Rotate the engine by hand. watch the #1 intake valve rocker. When the valve closes, continue to rotate the engine until the timing mark on the damper aligns with the TDC mark on the tab. The rotor should be near the #1 position on the distributor. If not remove the distributor and reset it to align with #1.

thanks randy, looked at that. the TDC mark was right on the piston was up and both valves we're closed. i checked the resistance in my wires last year and they we're good. maybe my rotor got cracked in all the moving around?? john

Check for vacuum leaks. I once did a intake swap and when I went to fire it up, it was backfiring thru the carb. just as you described. Started double checking everything, and it turns out that I either missed torquing down a couple of intake bolts, or they somehow mysteriously backed out. Tightened them up, all was well.

If your gearing down and you backfire then check your power valve if it's a Holley. I've also seen a bad condensor or points cause a backfire while trying to start the car, if your still running with them.

Mark

John go through the firing order it is easy to get crossed up,maybe you missed one...FRED