Hey Guys.

I've got a new YS 91 with about 10 flights on it and I'm having the same problems! This is my 3rd YS and the only one I've had a problem with.

Ive always used 30% heli fuel and an O.S. plug. I installed the engine in a WM Dago red, inverted. I had fuel leaking from the carb but it ran great. I took it to the field a few days later and fuel was still leaking from the carb. The engine started great, but would surge up and down at idle and would die.
I richend up the low end about 1/2 turn and it idled great.
I took off made a complete flight and the engine died on final.
I went home, checked high end needle was1 1/4 turns out.
I reset low end to 1 1/2 turns out and ran it with the cowl off. It ran great! No fuel leak! Let it idle beautifuly for 30 sec and punch the throttle. Excelent respose and power with no hesitation.
I put the cowl back on and flew it the next day again a dead stick landing.
I refueled for a second flight and the surging came back. Shut engine down and richened low end 1/8 turn and it seemed to be better. I put on a great flight and a dead stick final along with a strong gust crosswind cost me the airframe.

I don't know If I should try re-tuning the engine or send it in?
Tuning hasn't seemed to work.

Thanks
Jeremy Smith

With the hot weather upon us now, I'd say the engine is just overheating. Drop back on the nitro and go to less prop. Let the engine wind up a bit and it will run cooler.

Let me know how it works out.