I would appreciate any suggestions regarding my difficulity getting my Saito 150 to run consistently. Here's the story.

Engine is about two years old and put it on a Ultra Stick. Broke it in as per the directions. Using 16 X 8 prop and 15/18 Wildcat 2/4 cycle fuel. Engine broke in fine and ran perfectly for the first gallon of gas. All of a sudden it started throwing the prop. Lost several and a couple of tru turn spinners. This was happening at different needle settings. The "experts" at the field were stumped and suggested that I send it in to Horizon. Did that and they returned it stating that it tested fine on their bench. Mounted it on the plane again and got several good flights. On the last flight the engine quit at a very bad spot. I tried to save the airplane but ran out of altitude and airspeed and wrecked the stick.

Just got another stick completed and went out tonight to test the engine. Engine started fine, good idle and transition but at max power the engine would run for several seconds then quit. Someone with more experience than had took a look and he tried the engine at various high end needle settings. Started at 1 turn and did various increments up to 4 with no difference in performance. At richer setting, engine did seem to sustain a higher rpm before it quit. This other club member is now also stumped. Does anyone have any ideas? I am using a OS F glow plug. I am using a larger fuel supply line to the carb but remembered that I did not change the fuel line to the clunk to a larger diamater. I don't know if this would make a difference. Tomorrow I plan on changing the clunk line and putting the engine on the test stand at the field to see if it runs any better.
Since I am new to 4 strokes, this has me stumped and disappointed with my Saito. Since I have been in he hobby, this engine is the first one to give me headaches. I sure would appreciate any suggestions. Thanks in advance.