Originally Posted by Rocky_Motor
To learn, the best is probably a kit. You'll also quickly learn that almost everything in the kit is suggested to be replaced. NGK spark plug, better cdi wire and cap, new throttle+kill switch, better sprocket mounting method (depending on your situation)... But most of all, get rid of the included tensioner as fast as possible. Or modify it. More often than not, the tensioner will slide into the rear wheel spokes because it can't clamp properly. These engines can pose a lot of problems, but from a learning perspective you'll learn a lot from it. Some people here suggest taking the top end apart (head and the jug) and making sure that there is no junk ontop of the cylinder. I personally did this and found gasket material on top of my piston. It was also a great opportunity to re torque the head bolts.
And finally.. I would say blue thread locker is a must. You'll have bolts rattlin loose all the time without it and then potentially breaking studs. Of course there is a certain torque range where you may not need the threadlocker but I personally do not know what numbers those would be.
If you're confident in what you can do in terms of fabrication, you may feel up for getting a different motor. Mounting the motor is the hardest part most of the time for any engine that is not a "china girl" as it is called in these kits.
Certainly is fun. Now that I have put my kit together and have found that the steps I took have created a reliable bike, I plan on stepping it up this summer with a new build using a real engine with 9hp. Either dax's or a morini.
DANG....! Rocky_Motor You make it sound like these kits are not worth messing with at all.........LOL!
You do make some good points here, but the chain tensioner isn't a problem to secure at all, I've put over 1000 miles on the stock tensioners with out a single hitch if it is secure correctly by drilling a small hole through the tensioner bracket were i saddles the frame and continue the small hole into the frame just on the outside part of the tube and then insert a small sheet metal screw and it wont go anywhere.
I still run the kit supplied throttles on all my bikes, haven't had a failure yet, but you're right they are lite duty, but hold up pretty good as long as you don't get rough with them.
You're dead on the money about using blue loctite on everything, I also upgrade all the mounting hardware to grade5 6mm stuff and use cap screws for all the engine covers.
I figure it's a good plan to just count on spending an extra $5 - $25 on hardware and possibly a couple other upgrades on top of the kit price, my first build didn't get any upgrades other than better rear mounting studs until I had about 1200 miles on it, rear studs are the only thing that ever failed, so I replaced them after 2 years of running this bike they haven't been touched since.
I know there are better engines out there like you mentioned but for the money if someone knows what they are doing these china girl are a good deal and cheap and easy to maintain, oh and did I mention lots of fun......!
Here is one of the ways I set up the kit tensioner bracket, this thing is bullet proof, I make the tensioner rollers up myself, which are much better than the kit supplied ones but not neccesary to have, just an upgrade down the road.