White spacer mod won't fix your cut out at 65.

There are 2 possibilities that I hope you don't have... electrical or cam.

and it could be just a safety acting up... bypass your kickstand safety as if the spring is weak and allows the stand to drop at speed for some reason it will cut out the ignition.

Electrical... I not sure how to determine this (the following is all vapor), a bad TDI or coil might cut out when pushed or maybe the starter signal to the TDI is still on keeping the advance off.
But a bad sparky will fail at higher pressures, so you might try a new one.

And finally, Cam... if the PO replaced the cam chain and did not set the cam right, previous posters have said it won't go pass 55.

Haven't had anybody describe it to do so.

When I had (no don't clean it... no don't clean it... ok, that's it, clean it) a sticky slide, you'd twist the grip and nothing would happen... till suddenly it'd open and whoa nelly she'd take off.