I have that exact same engine. Bought it a few months ago. My kit was missing a few insignificant nuts, bolts, and the front engine mount strap but for $106 to my door.... I can't complain. I used stuff I had on hand here.
I do not use it a whole lot. I've had it 3 months or so and the engine now has 300+/- miles on it. It runs remarkably well. I've run it out the box and on the bike except for changing the clip position on the slide needle and an NGK plug. What I mean by running well is the engine has always started easy, idles well, has decent mid-range torque, and the absolute top speed is 30-31 mph. I have a 26" bike and a 44T sprocket.
It's had a few carb issues and a leaking base gasket but all in all things have been good so far. Time will tell if it stays running correct.
This is my first go round with a motorized bicycle. Prior engine and motorcycle experience has certainly made it easier to get this engine mounted and stay running. I would think no matter the brand of bicycle or engine this hobby will take a fair amount of hands-on fiddling to keep it going.
When I first got it rolling, after break in top speed was about 27. Anything over 6000 rpm according to the tach and the vibes felt way too bad to push it beyond but it had a good bit of throttle left. When I took the cylinder off to repair the base gasket leak, I cleaned out casting flashing in the intake and exhaust ports. I also cut the intake gasket hole to match the intake port hole. I put it all back together and now I'm able to get up to 7000+/- rpms and top speed is now 30-31. I am not sure whether cleaning ports up or sealing a base leak is the reason for being able to pick up 1000 rpms and 3-4 mph. The high rpm vibrations are way lighter now and definitely up above 6900 rpms.
