so i've read a lot of the posts about the sensitivity of the 64cc polini. and i can testify that this is true (i seized twice, once broke the piston ring, and more recently slightly and only enough to stop the engine).
so i now have the cylinder with one "soft" seize history (sold my first polini kit after the first seize).
now i have a "B" cylinder with a "B" piston. i have a 21mm dellorto, malossi 4 petal intake with dual stage boyesen reeds, e12 filter, proma circuit pipe, hi comp head. 102 main, 60 idle jets. b9 spark plug. minimized the number of fins cut off the polini cylinder (kept all the fins on the head)
no air leaks, everything runs well. almost 100 miles with a new piston.
however, at around 40mph, when cruising, if i lay off the throttle, i feel the engine slowing me down. it sort of feels like a "pre-seize". like there is friction between the piston and the cylinder. i have 30:1 gas oil mix, think i have a pretty rich jet and the plug looks like a dark coffee color.
i am impressed with the acceleration (my front wheel lifts off sometimes) but past 35 mph, the bike engine just doesn't sound good, especially when laying off the throttle at a higher speed.
and it has always been this way. thanks for reading...if you have any ideas on how to improve this/tune it better, please share.