I have a Super Stick 60 with a O.S. Max .65 LA engine. When I take all is good until about 3 min into the flight. After about 2 min it starts to spudder like it wants to kill. I land and check it out and I notice that I have a lot of bubble coming from the line that comes from the tank to the neddle valve. I've change the lines and still get the same results. I am at the point where I want to just change the engine out. Any help will be appericated.