While both Elektrey and thatcrazyguy are both right, you may need to keep an open mind, as to how you change the roller weights, and clutch springs (and even the rear pulley spring).
You need to know how you want the bike to perform.
The rollers have a greater effect on overall gearing of the bike.
Lighter rollers will delay launch to higher RPM and tend to lower the gearing, making the bike 'across the throttle range' very peppy.... but potentially with a lower top speed.
Plenty of people prefer that, but a higher top speed could be re-achieved, with a stronger rear pulley spring.
So you'd gain low to mid speed acceleration, while regaining higher gearing for top speed.
Changing the clutch springs for a stronger type, will immediately delay your launch by 1000 RPM (or 2000/3000 RPM depending upon spring choice).
This has a lesser effect of lowering the gearing...... and it may be, that once in the powerband, you might not need to lower the gearing further with lighter rollers.
If you have fitted an expansion pipe that allows your motor to rev higher, then lighter rollers will be great, as the higher revs will use the extra gearing provided.
But overall...... if you just want to delay the launch, until your revs are further into the power band (by 1000 RPM) then, changing the clutch springs is the way to go.
My experience of this is very immediate.
With a few other members, we are working on a project that is just this weekend, at this phase.
We are trying to make launch earlier.
9g rollers to 11g rollers gained us
only 200 RPM.
We were looking for at least 400 - 600 RPM gain.
Rollers clearly have their part to play..... but if you genuinely want a delayed launch..... then modifying the clutch grab point will deliver that directly.
Note: If you are into home engineering/tuning (or wish to get involved), you could consider this methodology to modify your clutch grab point:
49ccscoot.proboards.com/thread/12247/clutch-tune-desired-performance-springs
