Hi all,

After many years of 2-strokes, I decided to try a 4-stroke. I am now the proud owner of a YS-63s.

The situation:

YS-63s with 11x8 prop. Fuel is 5% nitro with 15% full synthetic oil. I setup the low and mid range per the instructions and everything is fine up to about 2/3-3/4 throttle. Above that, the engine sounds like it's bogging down and I hear what I would swear was metal-on-metal "clacking" sounds. I pulled out the tach and played with the high needle and found a "peak" at 10600 rpm, but still get odd behavior (surges, sags, metal sounds) at full throttle. I've also reset the gaps on the valves using a piece of paper as a gauge. I've run at least 2 gallons through it.

Of possible note, there is very little exhaust smoke until about 2/3 throttle with a steady increase in density up to full throttle at the "peak" setting. If I lean it one click further, the engine looses power and makes more and louder "clacking" sounds. richening even one click seems to sap power from the whole throttle range above 1/4 stick.

Is there anything I should check?
Is it considered "broken-in" yet?
Is the high needle supposed to be this sensitive?

Any help, hints, or commiserations are appreciated.

Thanks!