Originally Posted by rmarshall234
Maybe the third time will be the charm...
One comes out the air filter and the other out the tailpipe
Yes, we can keep telling the OP that (or maybe it was directed at me), but it is hard for a novice to understand the nuances of each of these and discern the difference in sound. The OP was sitting in the cockpit, so how would he know which orifice that the explosion came from? Best we just give him diagnostic aids based upon the likelihood of both. Excluding start up events, backfires at medium to high power settings (where the OP's symptoms begin) are uncommon without serious issues with the valve train or serious issues with ignition timing, so we can assume these were afterfires, as it starts and runs fine for 10 minutes before the issue reappears.
And yes, I know that the over rich or lean will cause afterfires, not backfires. But I am using the terminology that the OP understands. The vast majority of people call these backfires and as diagnosticians, have to work within the operators knowledge level.