once in a while when i stomp on the gas it will backfire through the intake. not much, just a little puf and then clears up. it has a new edelbrock 600cfm 1406 carb and a stock 305 intake with an adapter. i don't know what it could be. could to much backpressure cause backfireing? it has crappy 305 manifolds right now and there is a ton of backpressure. i put a peice of sheetmetal (about 1/16" thick) over the egr port and it made a bubble in it about 1/4" high from the backpressure, would normal backpressure cause this?

 

Check the timing, choke setting, and make sure your plug wires are in good condition.

 

Using a square bore carb with an adapter on a spreadbore 4hole
manifold isn't exactly the best for fuel distribution.
You bound to get a lot of fuel shear. and erratic fuel flow patterns at different throttle openings.
Any exessive exhaust restriction surely isn't helping either.
Other things to look for are Over heated plugs (heat range)
low octane fuel, Bad secondary ignition system (plugs, cap, rotor
wires) Over advanced ignition timing.

You've been posting a lot of questions about this and that.

When you get rid of the funky stock intake/adapter and stock exhaust manifolds, you'll find you then will have a whole different beast.

Till these critical areas are improved eveything else is just academic.

All the high $$$ heads, cams tuning etc. won't do squat with these performance bottlenecks.

 

the timing is set at 12*. any less and it will backfire more and the idle will go way down and it wont respond good. the plugs, cap, rotor, and wires are all new.

i can't wait till i get the new intake, and have the headers put on.

what is fuel shear?