help with misfiring

i have a 350 with a 750 holley carb on it. when i gun it it misfires past 4500 rpms and then as soon as i let off it backfires. is this to lean or to rich of a mixture.

first do you have an exaust leak anywhere
second how about some info on the motor
could be a number of things
high k motor it could be cam
exaust leak
valve adjustment
spark plugs, wires,cap and rotor
coil ???

i do have an exhuast leak. my headers do not seat well and there is a little leak on the drivers side.

what i'd look at is timing, shoot a timing light at it and see what it looks like. and next, the coil might be worthless

That 750 Holley, unless it's toast, should easily feed that 350 up to the redline. Check the coil and wires.