[hobgoblin351]

I was driving yesterday and started backfiring through the carb. Or what sounded like a backfire. Got it home and checked it out. If you rev it slowly it's ok until about 1/2 throttle, then pops. Slap it open and it pops right away. I played with the timing and it still pops. It's a relatively new engine, about120 miles, and running 10.25 compression. I did'nt have this trouble last season. I took ti out of storage and ran it with the old "winter" gas and it ran fine. I put in some fresh Mobile 1, 93 octane and it started soon after. Haven't tried octane boost the stores were closed. Could it be detonation? How would I know for sure? Thanks