.22 rifle shot?

Check to see if you blew a spark plug out of the hole.

Backfire through the carb? I've had that happen and it sounded like a high shrill backfire.

2nd Mustang said:

Backfire through the carb? I've had that happen and it sounded like a high shrill backfire.

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I agree my friend has this problem in his new camaro, we are still in the middle of tuning it but damn when that thing backfires through the carb. Sounds like a gunshot and then a foot of flames out the top. It is a bigtime timing issue that causes it most of the time.

TBP have you been able to confirm what the problem is? I have a '70 Mach One w/351 Clevend w/orginal heads 571 lift cam 220 degrees, MSD rev limited to 7000rpms, 650 Holley daul feed, 2500 stall and 389 drag posi. The car ran great with 112 octane and now with 93 octane lately because I have not had the time to fill with the higher octane. Nonetheless my Mach One ran fine with 93. Twice the backfire ocurred thru the carb under idle with tap of the pedal because it would hold ~1000rpms, too high. Also I noticed that in 2nd gear (automatic) it runs rough at about 3000-5000rpms. Now I raced a newer Mustang rolling at about 40 miles per hour and then I shifted down to 1st and hammered the engine. I forgot about the rev limiter and cut power. I shifted out and met the Mustang at a light and asked for another chance. I was gone in seconds and he was left in the dust in a big way. Did I cause an issue with the timing-timing chain stretch or lost a tooth? My 351 runs without a tick in the valves it is so clean. But I can feel a difference in second and backfires "at times" at idle.
Any thoughts would be greatly appreciated.