I almost had to reread this entire thread since I assumed, by the amount of engine problems, this was an MDS thread. Kind of suprised of the negative experiences people are having with some OS engines.

Nik, what do you mean by "maybe the needle valve"? It sounds like you are runnining your engine too lean and I'm guessing if it isn't a partially clogged carb or a fuel delivery problem then its gotta be your needle settings.. Rotate the large needle valve sticking out of the carburertor in the counterclockwise direcdtion about 1/4 turn and then verify you are slightly rich (about 300 rpm shy of max lean rpm) with the pinch test (do a search here for pinch test). You probably are wringing out your engine on the ground and when you fly, the ever decreasing fuel head causes a similary increasingly lean mixture througout your flight until you reach a point which results in a too lean mixture and a deadstick.

The OS engines are extremely user friendly and switching to another brand for future purchases will not help. This is a great time to learn how to tune your engine.

A fuel filter inline with a fuel line to your carb is another failure point. Your are better advised to install one in your line from the fuel pump.

If you suspect the carb is dirty, just remove it, take it apart and clean it throughly. Yes, you can even use water and dishwashing detergent to clean it. Just lightly oil everything when you put it back together.