lrb75

My Feedback: (12)

I have a YS91 AC that I picked up slightly used. I tried to start it for the first time and was pleasantly suprised that it fired right up. It even sounded like it was more or less in tune. I advanced the throttle and it picked up speed up to full. I lowered the throttle and it went to midrangeat about 3/4 closed and continued closing the throttle and it went back to full power. Hmmm. I reset all the needles and regulator to the recommended in the manual and then tried the settings recommended at YS performance. Checked the valve clearances. No changes. I understand that YS engines are sensitive to air leaks but I was getting full throttle with the barrel fully closed. The orings seals and gaskets all look fine so where can enough air be getting in to let the engine run at full throttle?? Over 8K rpms with the barrel closed seems impossible. I have another identical engine that I have sucessfully run but this one just doesn't seem right. Any suggestions?? Thanks.

Richard L.

My Feedback: (24)

You definitely have an air leak, probably through the valve cover gasket. Are you sure the barrel was fully closed, as clearly seen by the eyes and not felt by the throttle arm because the throttle arm can come loose?

lrb75

My Feedback: (12)

The engine was on a test stand so I could clearly see the carb barrel.

d_bodary

My Feedback: (85)

The easiest way i know of to find an airleak on a YS motor is to drill out a old glow plug and solder a piece of brass tubing to it. blow into the brass tubing while spraying soapy water or snoop around everything including the rocker covers. any bubbles you found a leak. fix it and try again.

Dennis

lrb75

My Feedback: (12)

Sounds like an good idea. Anyone have an old glowplug. I don't know if I have one laying around. I tend to throw them away so they don't migrate back into an engine

d_bodary

My Feedback: (85)

Just go down to your regular flying field and kneel down. Feel that sharp pain in your knee. Yup that one now look that is probably an old glo plug that someone tossed down on the ground. If all else fails PM me with your address and i'll send you one.

Dennis