How to lower the RPM at high speed?

[skywriter]

Given BSE 125 cc motard with Lifan 1P52FMI-like engine.
What's really annoying is painfully high RPM when riding over 70 km/h.
The engine really needs 5-th gear.
Is it possible to find anywhere and install the engine with 5 gears instead of the stock one?

 

[SwapperMX]

How much have you played with final drive gearing already ??

 

[my67xr]

You can buy 5 speed gearbox's that will fit your engine but hey are expensive.
Takegawa 5 speed Transmission and Manual Clutch Complete Kit - Takegawa - Pit Bike Parts


Fit a bigger front sprocket and/or smaller rear and adjust/shorten your chain to suit.
You may even be able to fit a taller profile rear tyre?
The engine will lose torque taking off with higher gearing though, and may not have enough power to keep the bike at a constant faster speed.

Other thing you could do is to fit a bigger engine, the Daytona 4V 150cc/190cc engine's 150F/150FDX/150FLX 190F/190FDX/190FLX will certainly help your top speed too.