I am trying to convert my crappy little electric dirt bike
This is a very true statement only because of the attempted conversion, it is a perfectly good ELECTRIC BIKE..........
Even if you have the tools and the ability to get this conversion done you will not have much of anything for all your labor....and busted knuckles IMHO.
The entire mechanical make up on that little bike is way wrong for these China Girl engines, the brake is on the wrong side, the drive sprocket on the wrong side, the swing arm will wreck your ability to make an easy simple drive system, it's just not a good platform for these engines and would maybe give you a 15mph cruiser with that tiny rear wheel & tire........
What I would do if I really wanted to have this thing gas powered would be to just build myself a pusher trailer with a HF 79cc or one of the up and coming 99cc engines and then you could get rid of all the electric stuff and still have that good rear brake and have something that could be geared to zip you up and down the street @ 25-30MPH possibly if set up right, a very small pusher could be built for that little bike, and would solve all the headaches your having right now that will not end IMO on that little motor bike.
OR better yet just put a China Girl on a BICYCLE if you dont like the pusher idea...then make it a legal MB that way....
Below is a couple of links to a simple pusher set up that could be put together for your current Motor Bike....
http://www.youtube.com/watch?v=pSngBqZd9VA
YouTube - Morotized trailer in Hawaii pushes bike 35 mph
YouTube - Mike's 196cc push trailer demo this kid has a couple things wrong like on the 8-9hp when in reallity they are rated at 6.5hp stock, but he made himself a nice little ride here accept for that no-flat tire no way that will last very long.
Anyway just some ideas and my opinions, nothing more nothing less and I dont claim them to be worth a lot ta-boot....
Peace