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....

the needle valve Oring is bad!!!
i had the same issue!!!!

try to put as new one with addtional silicon tube all over the needle as well to prevent air-sucking...

gadix

You may want to see how well the engine's cooling. If it's not cooling well, the case can transfer enough heat to the needle assembly that fuel can vaporize. You may also be getting vibration-induced fuel foaming. That means that the air in the tank is being agitated into the fuel. This causes micro-bubbles that you won't see until they accumulate and then break off at the needle valve.

could this bubbles in the tank, come from the back-press of the exh?
thx
gadix

Check and make sure at the needle valve housing that the needle housing/banjo fitting is tight and the cap plug [where you can reposition the needle valve assy]. One of mine had a leak there causing bubbles.

Thanks BAX that was exactly the problem.....The engine was heating up due to cowl.....a small amount of the head fins were exposed to the air....I took the cowl off and the engine runs great now...a lot of power....Thanks for solving the problem....

DRAGUNOV