I have several ys engines and love them,however I bought a used 53fz and it is giving me fits.Its runs strong and idles like a Swiss watch,but every time I change throttle settings I never achieve the popper high end needle setting. It can be all leaned out and running great,then shut the throttle and when you open it again it is too rich,do it again and then its lean .All I do is chase the needle around.
Fuel is 20/20 plug is OS#f prop is a 12x6. I have two 63 that run perfectly on same fuel.