this could be interesting,
Well on the ft160 i have grinded the slot for the low end of the throttle as you showed me bert..so there would be no side movement of the throttle barrel until near half throttle roughly..basically a set mixture to a degree..
When i ran the engine for awhile..yes i noticed the left cylinder (from behind engine)being rich on idle and 1/4 throttle, probably up to half throttle, it would be noticeably richer than the right cylinder..
when above 1/2 throttle it runs rather even and clean on both cylinders..
could it be something to do with offset cylinders and variations in each intake pipe that causes the fight for even vacuum on each side..