I got a second hand TT91 4C from a pal, he changed the piston, sleeve and bearings. Also, got the valves etc adjusted. He is good at such things. Today I tried to run in the engine. It had problems.

1. Engine idles when the carb is HALF open (2,700 RPM);
2. Engine peaks at 6,800 RPM with an APC 15x4W; and
3. Engine peaks at 6,200 RPM with an APC 13x6.

Running Cool Power 15% Heli fuel, OS F plug (new). I am lost as to what the problem is, it will start easily but why the above problems? I need some help ... thanks!!!