Hey all, I’ve been having this problem for a couple years now randomly, I’ve tried the things I’ve thought were the issue and it’s still a problem so I figured I’d make a post on it.

Ive got a 350 sbc in a 1966 C10. The motor has always run pretty good but it has an intermittent issue under heavy WOT load. It will essentially hit a wall and won’t go any farther. Last night it was about 3300rpm and it wouldn’t go any farther. When this happens and you back off the throttle you can hear heavy backfiring from the exhaust. Sometimes this happens at higher rpm’s, it’s been completely random. I’ve tried plug wires, and adding a fuel return line (thinking it was a fuel boiling issue) due to the humid climate I’m in. It’s still an issue. I’m starting to think timing or accelerator pump but I’m not sure. I don’t know the cam specs as the motor hasn’t been touched since the 90s, I just know it’s on the mild side. 650cfm Holley carb, I don’t remember what the timing is set at currently I think it’s around 30° advance, vacuum isn’t hooked up on the distributor. Thanks!