For what its worth, I have 2 of these Stage 2 Cag type pocket bike engines on 2 of my motorized bikes & although I have done a bit of tinkering with them both to solve the loosening headbolt issues, they have been running really well & start on the 1st or 2nd pull everytime. I was running a super reliable Lifan 2.5 HP 98cc 4 stroke that this little engine has replaced. Everytime I take them out, I cant help but ring the revs out them like a kid again & grinning from ear to ear. I'm guessing it @ around 4 hp & just over 50 mph. Yes, loud as h*ll with the pipe, but the perfect lightweight (~ 6lbs) powerplant for a MHPB (motorized high performance bicycle). They can also be mounted right up to any friction drive kit using the 4 clutch side holes or DIY mounted using the 5 bottom mount holes.
Priced at $125.00 without a fuel tank or exhaust pipe