i have a 63fz that runs great about half the time. it will be running great then throttle back to slow down then throttle up and the thing lays down till it clears the fuel then runs good. it dont do it all the time. then sometimes when landing it floods out and dies . i have run the valves several times and cleaned the reg. it seems to be a problem with the reg. not seating all the time. i have it set almost bottomed out. thats where it runs the best. then sometimes i get black oil on the side of the plane and its not comming from the muffler it seems to be coming from the carb like the intake valve is not seating all the time. but then sometimes the thing runs like a swiss watch, i have 5 ys engines and this one is kicking my ass. when it runs right it is a beast for its size.. i have been putting off writing you because i can usualy figure these things out i have been wrenching for a living for 30 yrs.lol what do you think
earle