Lukas, it seems to me that if you make a speed run, then a lighter, more compact rider does, and gets the same speed, you must be running up against the cdi limiter, or, the gearing is the limitation.
Start doing the math on sprocket upgrades and see where the optimal balance is... Crudmuffins! That ain't gonna work, here, is it.
OK, over-inflate both tires when She runs... Then try a taller tire, on the rear drive tire.
It's possible, since the goal is top speed, level ground, you might shave the inside of the front variator so it closes together a little more, which will increase your ration and go faster.
Make changes to the rear variator so it does not close inwards fully, to create a ratio better for high speed.
...and all this is gonna destroy your low end capability. Sry...
redk