Operator malfunction...but no barb from me.
I've got a jewel of a 1/2A plane (flapped Keil Kraft Radian) built by a British chap. He wanted a surrogate flier and sent it my way. While I could bench run the low hours Medallion .051 with high compression glowhead, any time it got in the air it absolutely floundered. I mixed a bunch of different blends from 15% Vitamin N up to the latest ~23%-25% brew. If it ran a tank out, it flat raced out the lean run at the end of the tank. Needling for just off lean was almost impossible. I changed fuel lines, flushed the tank and NVA and bench ran it some more.
I talked the runs over with FredV4 last weekend., and he asked "any chance you have too much compression?" Hmmm.
This morning I added two glowhead shims, and ground ran another couple of short tanks, each time I wound the needle valve in 1/8 turn. After three tanks, I checked tach at 16,700 and lined up the camera...and ripped off four solid flights. I ran the needle in maybe another 1/2 turn or so. The engine needed a prime to start now. The worst part is knowing I was scared to fly it for the last four years because I couldn't trust the powerplant. The best part is I can really play with the plane now! Yes, I have video to prove it.
I will mix up some 30%N for the next outing. Don't be afraid to make changes to your engine...add a few shims, change your nitro ratio, change your oil. But adding/removing shims is easy and fast, so it can be done at the field.