Dave,

I have a YS 91AC which was sitting on my shelf since 1998 before it found a home in my latest mini pattern plane only recently. It is my first YS and nobody at the club has any experience with YS either. Power is GREAT and the throttle response is simply awesome. There is just one point I wanted to check. Even with 2 -3 clicks off the peak I have to set the needle valve only at 3/4 open. I have plenty of exhaust smoke with this setting. The needle adjustment between very rich to (too) lean seems somewhat critical at this point. However, as I said, I have no comparism what is normal for this engine. Since the transition from mid range to peak goes without much of hesitation I have not fiddled with the regulator (yet). The regulator bolt is flush with the casing. I am still stunned about the acceleration anyway which is no comparism to any other engine I had before.

Are you aware that the needle valve design has been changed over the years to a more gradual taper?

The fuel, I am using is a fresh mix of 25% nitro and 23% sythetic.

Thanks!