before you consider how to make your bike faster, consider how to make your bike safer, easier to ride - bigger brake calipers/discs/pads, steel brakelines / adjustable, more progressive suspension / keeping your headlights on all the time / better tires that grip instead of slip
change the roller bearings for lighter ones, they will spin quicker, allowing for better acceleration. acceleration comes at the expense of top speed.
- Open airbox, new needle & jet kit for the carb, free-er flowing exhuast. totally ditch your air filter…air here is filthy, but honestly, how many years are you gonna use your scooter…2 years, 3 years, maybe 5? With more oxygen flowing through the carb, your bike will run lean(or ‘hot(re4)’ as the local mechanics say) so you want to play with a combination of a higher needle position(you can throw washers underneath or get an adjustable position needle) and larger main jet. too big a main jet or too high needle position results in a soot-inducing rich air-fuel mixture(‘cold(leng2)’ in local mech-speak) which not only pollutes but gives horrible fuel efficiency(burning more fuel per unit of air than needed) air temp, altitude, humidity all play a part in determining the proper settings for your bike.
aftermarket exhaust does almost nothing except make more noise and attract attention from thieves. get your current exhuast cored-out and welded back together. OEM probably gives you the best bottom-end torque at the expense of top speed, an unbaffled straight pipe from the engine has no bottom end torque, no noise control and no place on a street bike[btw - emmissions is adjusted via your carbureted air-fuel mixture, not the exhaust…so if your carbs properly dialed, you’re good to go]…improperly dialed carbs/leaks anywhere from in-to-out/straight pipes are a good combination for backfire, not a good thing.
aftermarket carburetor is the single most effective way to enhance performance. butterfly valved CVs aren’t bad, but for real fun get flat-side carbs…popular CVs are CV24 to CV30 - the # is the size of the opening…smaller the opening, the quicker the gases flow thru - you may find the smaller opening to be a bottleneck at higher/top speed.
local 250cc scooters come with CVK30(CV30 made by Keihin, thats what the K stands for) so theres no need for any 125/150 owner to bolt on anything larger than the CV30…CV + needles/jets + installed by a competant mechanic may run you 4,000 to 7,000 depending on who you go to. if you’re good enough to do it yourself, its probably 3500 to 4500 for the parts. if you’re good enough to do it yourself, you probably stopped reading 5 minutes ago.
Flat side carbs are the absolute quickest way to ‘re-discover’ your scooter…you should look for PWK & FCR from Keihin or TM, TMR, TMR-MJN from Mikuni. WOW. big smiles all around. welcome to your new ride. may cost anywhere from 8000 to 30,000 depending on your need to demolish everything else on the street(within your cc class).
bigger cylinders/different pistons/cams are available for all of the popular 125/150 scooters. ask around. redwagon seems to really know his stuff in this area. adjustments in this area will need carb adjusting(needles, jets) as well.
you can get a quicker turning throttle holder so that just one small handful can let you run the entire range of your throttle - more useful at the middle to top end, hamfisted slamming open the throttle at the stop light isn’t so useful.
transmission gears can be custom machined if needed, however, this is like getting gold caps for your teeth - actual longevity is questionable and is it really worth it? the bike will be quick, but when will it fail/break, stranding you on some remote mountain road. i’d stick with OEM factory here.
kevlar belts are available for most of the popular scooter makes - these are tighter and less prone to stretching - putting more power to the tires instead of stretching the belts.
thats all i can think of now, good luck with your scooter, hope things turn out well and ride safe!