Scooter starts bogging at full throttle after a while...

[padly1995]

Hello,
My gy6 50cc scooter with drilled exhaust 6gram roller weights, 84 jet, needle on top slot and drilled out restriction tube in air filter, needle removed from auto choke, because it was failing...

starts bogging if i drive at top speed for more than about 1 minute... speed starts to fall and at the end scooter stops running! But if i let the throttle, so speed falls for about 5km/h scooter starts working again!

Another strange thing is that scooter usualy max it out at 50km/h (34mph), but some times (few times a week) in goes around 70km/h AND NOTHING IS RESTRICED SO IT SHOULD MAX IT OUT AROUND 70KM/H EVERY TIME :SS

I already tried jets from 79, to 87, all positions on the needle, with:
air box restriction tube (not getting more than 20km/h +backfiring),
with drilled restriction tube (current state)
and without it (slow acceleration, top speed about the same as with drilled tube)!
I am also sure that there are no leaks anywhere and that air filter and carburator are clean


So what can i try else? Thanks for anwsers