I’ve still not got my grimey hands on an upgrade for my pk 50 s, i’m looking at a 75cc kit, an new exhaust. Can’t afford the pollini 110 along with new crank, upgear, new carb…
So what i’m actually wondering is, will i need to rebore the port, and piston casing. Sorry if i’ve not got the terminology right, noob!

If you mean will the barrel fit the cases;D yes they will!
You can just bolt on, but most need the transfers matched to work properly.
Also upjetting(a bigger jet in the carb!) and might need the stator plate moving, but not sure on the 75?

„but most need the transfers matched to work“

I’ll investigate.

Cheers dog!

Edit. It was the transfers, that’ll need doing, cheers again!