OK, I am taking a break from this one. While I do so, I am looking for some input. This engine idles perfect, accelerates properly. But when I hold the throttle and try to maintain speed it bucks and cuts out. I haven't gotten it past 6000 rpm to see the upper range, still breaking it in. I have adjusted the valves, cleaned the carb, changed the plug to a NGK. I wouldn't think spark would be the problem since idle and acceleration is good. So I am ruling out the magneto. It has done this since install 3 days ago. Oh and I have tried to lean it out but no luck. The spark plug was black when I pulled the original out. Most importantly, when I turn the air/fuel screw in all the way, it revs higher and does not die like my other engines did. I guess maybe I will steal a carb of another kit to see if that changes anything. Be back with results on that one in about an hour.