bob8619

Saito FA-91S on Great planes quarter scale piper cub... Ok so sometimes I have this problem and then sometimes it works as it should. Breaking in my engine on the plane, have the vent line connected to the muffler and all that. I plug open the throttle all the way, plug the muffler with my finger and turn the prop by hand multiple times, sometimes that primes it and other times it draws it up and then I hear compression noise somewhere and the fuel gets pushed back towards the tank. I have noticed sometimes it seems to happen like this after its hot but not sure if thats a for sure thing. Another thing that helps, but not always, is making sure the tank is completely full. As I type it is full and I'm not able to prime it. I read in the engine manual that the center of the tank should be mountain no more that 5mm from the center of carb or something along those lines and I think my tank is probably lower than that, however it is mounted as high as it can go unless I build platform above the servos or something. Is this an engine issue or the tank height issue?

Thanks, Bob

bob8619

I may have found the problem. Possibly due to a slit in the vent tube. Which may also explain why it seemed to have been running a little rough today. Hopefully it didnt cause any damage to the engine...

jester_s1

Doubtful it hurt your engine, but a vent leak will definitely make priming a pain! I'm glad to hear you figured it out.