I own an OS 46AX. Purchased new. It was broken in exactly like the manual says. It has about 12 tanks through it. 6 flights, mostly at about 1/2 to 3/4 throttle. Seemed to run okay during the flights, but because I am a newbie, just very gentle flights. Very short flights, only used about 1/2 tank each flight (10 ounze tank).
Now I am trying to fine tune the engine. First I set the high speed needle. Run it full throttle, lean the high speed until the max RPM is reached and then richen until the RPM's drop about 5-600. At that point it runs really well for the first 1/3 tank of fuel after I made a very small adjustment to the low end. I thought I had it running really well. Transitioned great. The pinch test on the low end sounded great. Everything going great, then after like I said after about a third of a tank, it starts running real eratically. Speeds up without any throttle change, then drops back down in RPM. It almost sound like it's leaning out, then starts to run right, then leans out again. Moved the low end needle back to where it was originally, same erratic performance.
At that point, I emptied the tank, and put it away for the day. Next day fill her up, starts right up, first or second flip, runs great for about a third of a tank, then starts acting up again. This happened three times now, all three on the ground, not in flight.
Anybody have an idea what could be wrong? Brand new number 8 glow plug is being used.