Hey Anderw
Everyone chases the perfect engine run. Well anyone running IC engines. I'm still learning.
Just this weekend one of my flying buddy's had his engine go lean right after the horizontal 8's. Three flights and it went lean in about the same spot.
I have had the same problem with a clunk tank. The pickup line got a pin hole causing a air leak. His tank was metel. I suggested a different. He said he had swapped it out, twice.
My coached looked at his tongue muffler and said his holes were not big enough causing the engine to over heat.
Next step was to fly without the muffler. It ran fine. Drilled out the holes and problem resolved.
I learned something.
Glad your picking things up. Keep on keeping on.