Hello,

I have a YS91 AC.

I've had the engine in a few airplanes, and it's never really run right. The idle has always been perfect, and it starts easily. The problem is that no matter how rich I set the high end needle on the ground, it seems to lean out in flight.

The engine has been sitting on a shelf for a few months, and I'm getting ready to put it in another plane, so I've got it on a test stand.

I've got a 14x10 prop on it, and am running 15% Powermaster fuel. It's got an OS F plug. As it always has, it starts easily and idles great. When I run it up to full throttle, it winds up to about 8800 rpm, and puts out a steady stream of smoke. After about 5 or 10 seconds, the smoke stops and it runs really rough (rpms bounce between 4500 to 7000 rpm.)

At the moment, I've got the high end needle 4 turns out, although the symptom is the same, even if I turn the needle in to about 1.5 turns. The regulator screw is flush with the housing.

Any ideas would be appreciated.

Thank you,
-Wade