PatternCombatKid53

My Feedback: (7)

Hey,
I have an O.S. 70-FS Ultimate that I need some help with. Here is the story, about two weeks ago I replaced the head on the motor because the threads for the muffler stripped out. The valves were put back in according to the manual. The motor ran normally for a week and then I started getting air bubbles in the factory stock fuel line that goes from the pump to the carburetor. I replaced all the fuel lines except for the factory stock one. There are no bubbles coming from the tank going to the pump, but when the fuel comes back out of the pump and goes to the carburetor there are many bubbles. The motor runs fine up to half throttle, then the bubbles start forming when the throttle is moved above half. I am using an 11x5 propeller. Also, the high speed needle valve does not affect the motor, except when it is fully closed. I got the motor to run fine when I connected the clunk line from the tank directly to the carburetor. All the help with my problem would be greatly appreciated.

Thanks,
Doug Novelly

Bax

My Feedback: (11)

How well is the engine being cooled? Some of the FS-70 Ultimates have a difficulty in getting enough cooling air. You need to make sure that the lower half of the crankcase is also getting some cooling airflow, as well as good airflow through the fins of the cylinder and head. This engine will tend to run hotter than the regular FS-70, and fuel can vaporize in the pump if it's not cooling well enough. Sometimes, you need baffling to guide the airflow.

PatternCombatKid53

My Feedback: (7)

The motor is out in the open. There is no cowling. It has plently of cooling.

Doug Novelly

RVman

11-5 prop??