Hi Here's a problem I am unable to solve with my son's YS FZ110. After a crash last fall (no aparent damage to engine) and sitting thru winter and spring, engine runs at too-high speed at idle, even with throttle barrel ENTIRELY closed. As throttle is advanced above idle, rpm drops and engine stumbles. With patience, throttle can be moved to full-throttle and engine awakes to full-throated roar. Going back to idle initially produces idle rpm. But soon speeds up and back to before. Low-speed adj has no effect even if completely closed. Hi-speed needle affects high speed normally. Pressure regulator screw has no aparent effect. Fuel (with lotsa bubbles) can be seen going to carb with throttle at idle (to be expected because rpm is probably 3500 and regulator is opening). New CoolPower 30% heli fuel; OS 4-stroke plug.

I have replaced the diaphragm-the old one was stretched (BTW, does stretched d affect running?).

Seems to me that threre must be an air leak, preventing throttle from choking down the air supply thru the carb to slow the engine. But I can't find a leak around the carb, manifold, air box, or valve cover. We are still using the original, thin YS paper gaskets.

Am I on the right track with my diagnosis? Or is there something else that might be causing the problem? What should I do next?

BTW, I have read online YS info and believe that I understand YS 4-stroke operation. Except one thing. At idle, pressure system and regulator are not supposed to be supplying fuel to carb. Engine is running on suction, not pressure. There should be no fuel going thru fuel line from regulator to carb. Ok, so how does fuel get to the carb during idle???

Thanks for the help. Regards. -Gary