Stumble, Pop

I flew the plane on the 11th and halfway through the flight we started getting what I assume were backfires, about 1/sec. They were very minor "stumbles" with a pop sound. This was after flying LOP at that same altitude for about 10m.

Occasionally there would be a slight stumble with no pop sound. Power settings changes and changing to a richer mixture did not seem to help. After getting around 2000' AGL no more issues occurred for the rest of the flight to landing. Tested the fuel tanks for water again after landing, found no issues.

Flew it again on the 23rd and had no troubles until nearly leveling off at 4,500'. The mag check on the ground showed no issues but as I hit 4,400' I felt the first stumble and as I leveled off and started to go LOP the backfires started up pretty abundantly.

I didn't actually make it all the way to LOP before it started and so I decided to try ROP. Left it there momentarily as I started to turn back to KUZA to land. I swapped fuel tanks, tried the boost pump, and went full rich - none helped. Changing throttle settings didn't seem to help either, so I kept it throttled back. I did not try alt-air or an in-flight mag check (too nervous to do the latter). Again, once getting to 2,000' AGL (full rich) the engine was back to normal.

We have enlisted the help of Savvy MX with managing the airplane and they suspect a bad mag or plug(s). We hope to find out in the next day or two.



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