Hi again Fred:
I got a vibe that your problem may be heat related. You first, good, flight is the first one of the day in both examples. The second, bad flight is after the plane has been sitting in that very hot sun for an hour! What else had changed, NOTHING! Try keeping our plane out of the sun and in a cool place. Perhaps the fuel is also becoming too hot and thin leading to a lean running condition. Thermal runaway?
The above is just a guess. I have seen that combination run very well in cooler weather. The only thing that has changed is the ambient temperature. You did not fly it the other day when the temps were in the 90’s! The last time that I saw it fly was when the temps were 75-82 degrees. It few great that day!
Something to
Good luck,
Frank