350 sbc ,when engine is reved up o 2500 or more when i let off it pops or backfires through the header ,set timeing to many different settings and adjusted carb with no effect,runs fine till i get on it then it backfires when i let off
350 sbc ,when engine is reved up o 2500 or more when i let off it pops or backfires through the header ,set timeing to many different settings and adjusted carb with no effect,runs fine till i get on it then it backfires when i let off
350 sbc ,when engine is reved up o 2500 or more when i let off it pops or backfires through the header ,set timeing to many different settings and adjusted carb with no effect,runs fine till i get on it then it backfires when i let off
If it sat this winter I would guess crappy gas plugged something in the carb.Gas with ethanol is causing all kinds of problems in anything that sits.You could try using a can of Seafoam to see if that clears it up.
I tend to think these two are likely atop your issue. A vacuum gauge will do a lot of your diagnostic work on this one. You may have something as simple as a valve set wrong, too.
I tend to think these two are likely atop your issue. A vacuum gauge will do a lot of your diagnostic work on this one. You may have something as simple as a valve set wrong, too.
VB and the guys got you taken care of. If, what your saying you get on the pedal, and when you let off...theres a poping inside the header tubes, commonly refered to as 'rapping back', this acn be cause from cam timing, to the valve not seating, to too lean of a mixture and timing....you just got to narrow it down.
The major cause is usually the cam on a hi-perf. motor having the valve open slightly, raw gas already inside your exhaust tube, since the valve timing is holding the valves open a little longer at low RPM's, the pop is usually a by-product, either caused by the hot exhaust gases or by the spark coming later.
Timing is a funny thing, too early and you'll backfire thru the intake, too late and the perf. will really suffer.A backfire in the headers can also be caused by a valve being adjusted too tight (held off its seat)or a valve thats trying to hang up or gall in its valve guide.
Cams with alot of overlap will cause this, also....thats why some of them idle at 1000 rpm to clean themselves out. Anything lower than 1000 to 1200 rpm, and the motor is hyper-ventilating......
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