I have two new OS 50 SX engines.....both have the same problem.....when running at full throttle the fuel pipe between the needle and the carburator has continious flow of lot of bubbles.....I have replaced the fuel pipes but still the same problem.....the pipe that comes from the tank to the needle valve has absolutely no bubbles.....but even with those bubbles the engine seems to run fine but is less resposive to the neddle valve......if any one can understand the problem please reply.....thankss....