sgtcj

great.   Thanks for that.  It will surely save me a lot of time in research.

I had the same problem with a Chinese 110.  Seemed to be a wight issue.  When I rode the chain jumped off.   When the kids road (<100#) it was just fine.   Never could get it to stay on under load.

You can also add a screw with a lock nut to limit the thumb lever.  I've seen this on several models.

Good to know since I am about to order piston set for Honda trx.