Car missing out under load.

I'll try and keep this question short. Driving Car the other day(440-6 Superbee) and it started backfiring and mising out over 2500 rpm. pulled over changed out ballist resistor and everything seemed fine, drove another 30 miles no prob then on way back home bam!! started doing again, I just swapped old dist(dual points) out with Mopar Elect and fires right up revs into 4000 rpm range no problem idles fine,etc. went out for drive and under acceleration starts missing out and backfiring, let off and runs fine?? I've replaced the coil also with new accel superstock unit, new dist,cap,rotor,and ballist. so i'm kinda at a loss, Before the other day car has been driven alot with no problems.

plug or plug wire missing under load? EDIT What ECU?

It has the orange box ecu, and i haven't changed wires yet, they are a few yrs old so i'll do plugs and wires tomorrow.

Loose or fouled up spark plug,or loose plug wire.

A 6bbl car? HHmmm maybe the carbs need adjusting??
A vacuum pod stuck open/opening too soon on the outboard carbs and dumping fuel into the engine??

If carbs where the problem would it be able to rev so freely in nuetral? I can rev and hold a 4000 rpm and sounds good, but driving is a different story. Wires and plugs are on the to do list tomorrow.

4000 RPM and no load is totally different compared to 4000 RPM under a load,IMHO.
The vacuum rating is different under those situations and the outer carbs rely on vacuum to operate when the engine is under a load..

Here is the latest, replaced plug wires and plugs, gapped to 35, also changed fuel filter and rebuilt center carb, Still starts great and idles fine, but as before you take it out for a drive and when car warms up and you get on it!! low and behold, starts popping again let off and it runs fine, put 68 jets in and a 5.5 pv. like i said up until the other day everything was great then like mentioned driving normal to the car show and started popping and now i'm at the end of my knowledge.

I feel bad all that changing out & no fix (as of yet). I wonder if the intake bathtub gasket has developed a slight leak on the bottom side. Might richen the pri jets WAY up just for a test & see if that affects it & do you have another ECU in your stash that you could sub in for a day. That way no parts outlay just more time on it.

Yes I have another ecu, but it was doing the same thing with the dual point distributor in it, that's why I changed it out with the mopar electronic. Did adjust the fuel level it seemed to help a very little, We did richen it up with the 68 jets, Now it seems to do it more at full throttle before it seemed to go it even driving and just trying to accelerate, I think I'm going to swap the intake and carbs out tomorrow to a sinle 4bbl and see what happens

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I think I'm going to swap the intake and carbs out tomorrow to a sinle 4bbl and see what happens

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man that is a toughie, all the symptoms ain't adding up, we're missing something.