Starting to get frustrated on this tuneup. I have a 54 chevy with a 235. it has holley 390, split headers, pertronix ignition. i have been trying to tune it correctly for awhile. I rejetted carb and changed power valve to what is recommended from clifford performance. My problem is while driving at higher rpms, when i let off the gas, i get lots of popping and backfire through the exhaust. that is my only problem. the throttle response is good, no hesitation or backfiring on acceleration. I have timed the engine from 0 degrees all the way up to 20 degrees advanced. When I retarded the timing, it got worse. When I advanced it, still backfire issue. the spark plugs look good, not to lean or too rich. Only backfires from high rpm deceleration. Also it is not initially when i let off the pedal, its almost when the rpms get back down to about 2k. Any help would be great, I am not sure what it could be. Thanks!
