Exhaust backfire/popping

[dzwestwindsor]

Hello guys,

I've been having this problem for a while now, and I just can't get it figured out.

I have a 71 C20 with a stock 350, and it backfires or pops out of the exhaust when it hits around 2500-3000rpm. It pops erratically, anything between 1-5 seconds. It used to be worse (like popping during idle) but after changing the sparkplugs, it only does it in higher RPMs as I mentioned. It no longer backfires/pops during idle.

When I let go of the gas when I shift gears, it backfires/pops/gurgles a lot too.

However, once the truck has been running for several minutes and I get driving, the popping seems to be less prevalent, but still occurs on occasion. And it obviously still happens during gear shifts when I lift.

I know there could be 100 reasons for why this is happening, but I'm just wondering if anyone has experienced something like this before and could give some pointers from personal experience.

I think a key clue is that it only happens once the RPMs begins to pick up past 2500, and almost never happens at anything lower.

Any help is appreciated, thanks!

-David