I had a 350 built to 300 horse and swaped it from my 305, when i drive it when its cold it runs great bout when it got hot the motor backed fired through the exhaust as load as a shotgun, when i put on the throttle in isdle position it chocked out and backed fired some more. after letting the car cool off for a few hours it stoped doing it till it got hot(200-220 degrees) could it be the fuel pump? the fuel filter was clogged i changed that, ..please help

Here's an obvious question.Did you tune it?

yes it was tuned,

have you tried changing out your distributor? I'm willing to bet that's what it is...

well i changed out the distrib. to a new one, new fuel pump, filter,timed it before and after, the the results are the same bogging and a loss of horse power.i'm about to change out the wires and plugs but cross my fingers.

I think what he means is did you tune the computer. If not then that is probably your problem and you should take a look at the Free Tune Sticky in the TBI section. Happy Tuning

I changed the plug wires and found three of them were shorting out on the hedders. now it runs a lot better but i have to tune the computer now?

YES

do i have to buy a tuner or how do i go about getting it tuned? how much does either cost?