Oh that's why your bike is slow wayne.
Ditch that modded bx. Worst shifting ever. THA WORST
Either get the stocker Mitsuboshi from treats or endurance or get a half inch belt and run race gears. 16mm is too wide to shift right.
Only time a bx MIGHT be ok is if you're making insane hp with a 8k+ stall and even then it would still suck shitty balls(edited)