Hello fellas,

Acquired a .91AC for a H9 Katana right here on RCU. It looked like new (came in original box, no staining, solid compression, smooth bearings, clean valves and piston), so I am proceeding as if new. I installed it in the airframe, plumbed it as per the instructions (with Y.S. check valve), and set both needles to 1 1/2 turns out from closed, and set about running it in. VP 15% nitro, 18% oil, new O.S. #F plug, APC 14 x 8, uncowled. Here's what I'm experiencing: Start the engine, let it idle a bit, then run it up to set the high speed needle. It will not 'clear out' until I have the HS needle in one full turn (which is 1/2 turn out from closed), then, it 'catches up' and over leans, preignites, and spins the prop off. I have tried to 'sneak up' on the HS adjustment, only to have it do the very same thing. I don't want to damage this engine with preignition, but it will not clear out (8-stroking, as it were, if a 2-stroke running rich is called 4-stroking) no matter how I approach the HS adjustment. It idles beautifully around 2100 RPM, and will idle that way for a full tank of fuel if you let it. This is an older engine, so could it be the gaskets? What are the symptoms of a faulty or mal-adjusted regulator? Thanks for the help, I really want to fly this plane this weekend.

-Tommy