Hi David and welcome to the hobby. I thought I would elaborate on the reason a TT46 will out perform an OS 46 LA is because the LA has brass bushings to support the crankshaft where as the 46 pro has ball bearings. Also the carbs are different yours being of the air bleed type, The pro 46 having a low end adjustment as well as the high end adjustment, seems to help with transition. I'm not by any means an engine guru so maybe someone can explain a little better.