Old GY6 125cc to 160cc BBK timing issue

[sc00ter]

Alright, another thing(s) popped in my head.

You'll have to up-jet if you installed a bigger piston/cylinder kit. So if the OEM jet was a 105 don't reuse it. Go larger. There use to be a great website called Tuning Matters. His information on tuning is super helpful for inspiring tuners. I've used it several times to help dial in a tune.

After you get the motor sorted you'll next need to dial in the transmission. Your stock set-up will not like the bigger top end. The transmission will engage to early from the higher torque. But get the motor sorted first.

And you mentioned a ping noise. Did you do a compression test? If so, has your compression dropped any? Ping noise from the piston is bad! Usually a sign of an extremely lean motor. Way over-jet and go down till it runs. You'll also have to up-jet your idle as well.

We did a BBK kit on a Genuine Buddy 125. It went from a 125cc to a 161cc. Thing was death fast! I don't have the build sheet anymore and my old brain can't recall what jetting we ended up with. But anyone who did a BBK like we did on a Buddy will know what jetting they used, so that will give you a base line to work with. Elevation (like if someone from Colorado will obviously have different jetting than me on the east coast at sea level) will matter as well. A bunch of people have put BBK's on Buddy 125's. See in anyone has a build list on Modern Buddy for your base line jetting. The bonus is a Buddy uses a GY6 variant as well.