Posted by Sherman in Idaho [108.162.246.17] on Sunday, October 09, 2016 at 12:38:42 :
In Reply to: Re: Still no luck posted by Jerry in Idaho [162.158.69.92] on Sunday, October 09, 2016 at 12:07:49 :
It's a mystery at this point. Backfiring when letting UP the throttle while going downhill is usually caused by leaky valves in a tired engine. One question would be whether it backfires into the carb or the exhaust. Backfiring in the muffler means unburned gas is getting through the cylinders, so not a fuel supply issue. Backfiring into the carburetor (mild=soot on the choke plate, severe=carb on fire) means leaky intake valve or timing way off. I would check compression to be sure valves are good (still wonder if one is sticking only at high speed, though) and watch spark timing to see if it jumps around erratically at speed (advance mechanism acting up?)
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