I have a new FS26S. I installed it inverted in a .020 Cub. It ran OK for a while, then I throttled it down. As it came to idle, it began to run rich and quit. I cranked it back up and it did the same thing again. When I cranked it back up this time, it made a loud clicking/knocking noise, but cranked up and the knocking quit. Afterwards, in checking the play in crank, it had several places where there would be a noticeable knock. I removed the backplate to examine the con rod. The problem (and knocking noise) is that the piston moves up and down about 1/32" freely and makes the knocking sound at the ends of this travel. The con rod seems to be OK. I have not removed the piston yet. Could this be a broken piston or broken ring? Should I not run the engine inverted due to fuel accumulation in the cylinder?
Thanks for any tips.