Did you replace the points recently . The reason I ask is I had a similar problem and a older mechanic said start with the points so I looked again and I realized I had just replaced the points .The points were from Napa and they came in a box with two pieces .Now I am only a back yard mechanic and when I put the points on I thought the extra piece was for another application so the points went in and the extra piece stayed in the box .The truck started right up idled nice and off I went up the road sputter backfire when I pushed on the gas could not figure it out . Ended up feathering the gas to get truck into town a hour away . Was difficult .Turned out the extra piece in the points box was the spring and when I pushed the gas the points would bounce around without the spring and cause the popping and backfiring .If this doesn’t help then I hope you can laugh at my experience .Back yard specialist kevinski
