Stalling/Backfiring

[Mgicm]

Hope this isnt a problem to post here but have a 73 GMC stepvan with 350 sbc and auto trans. Keep having an issue with occasional backfiring and sometimes stalling out. Replaced fuel pump, changed to electronic ignition, new carb, plugs, wires, and starter while we were in there.

Truck runs well most times. We noticed that when it is hot out (90+ degrees) this seem to happen most often and usually in traffic. I am assuming that the massive amount of heat in this small engine bay is part of the issue. Has a fan on the radiator...not sure if a clutch fan .

My question is..what would cause a backfire through the carb out of nowhere after an hour of driving? Could the gas be boiling while we are in traffic and have something to cause the stalling? How could we move more air in engine area while sitting in traffic to help cool it down? That is assuming it is a heat related issue.

It is an older truck of course so the mechanic is starting to blame other things like engine components but i dont see how thats possible when the truck runs fantastic most times..very smooth, nice response. it is just at times it decides to stall out or even hesitate like no gas is getting there.

yes..we changed fuel filter 2x.


thanks! GP