Before you start messing with it, you need to confirm rpm or Hz and actual output terminal voltage with a DVM. Starting to mess with it could make things worse.
Unusual for that machine to make more volts than normal, but it is possible. Unusual for rpms to be high (and that can cause high volts), but that too is possible.
You need to buy/borrow/steal a digital volt meter (best if shows Hz), and if no Hz setting, you need a phototach.
Adjusting things before you actually know what it is doing is not the right way to sort this.