carb backfire under quick throttle

hey guys,

i have been pulling my hair out for weeks now because i cant get my truck running properly. here is a rundown of whats happening...
when i got the truck it idled very high so i tweaked the idle adjust screw a bit and played with timing.
under sudden throttle it would backfire out of the carb.
so i reset everything back to where it was and it would still backfire.
eventually, after checking the timing 1000 times, checking fuel system, sufficient spark blah blah i decided to get a weber conversion.

threw on the weber carb, started up no problem, but under sudden throttle will still pop out of the carb.
slow gradual throttle i dont have a problem its only a quick shot and it will pop.
also if the engine is under load it sputters out and is undrivable.

anyone else have a problem like this? im running out of ideas

I know you mentioned a 1000 times checked on timing. So you did the check crank shaft pulley mark at TDC and the timing belt cam gear marked #1 is aligned with 12 o'clock mark? Also was the distributor rotor pointing at the #1 spark plug boot of the distributor cap which is at the 9 o'clock position? So all these are lined up as I described? Also you checked the spark plug wires on the cap's firing order is 1-3 4-2 in a clock wise rotation?

Have you checked your exhaust system if it's clogged?

The weber conversion somewhat helped but still a back fire and won't go and sputters along...It could still be a timing problem or a clogged exhaust...

I've also made some mistakes and overlooked it a few times and corrected the issue resulting in a feel good moment.

timing has almost always been an issue with backfiring. if not timing, then somthings clogged or your not burning fuel right.. even a tooth off on the dizzy will do this.