utilizing the gears for the motor? Sometimes that's not legal in some areas to use a shift kit.
Cheapest way, get a chinabay kit till it blows then look for your next choice in engines. btw it's never inexpensive. Bike parts fail, engine parts fail. This was the worst hobby choice for me personally (No life, nothing to do havn't even owned a bike since a kid- I built my mountain bike motorized bicycle with a **** cheap bike my friend gave me in pieces for 10 bucks, then a 130 dollar custom kit with 33cc engine that had a bad carb rebuild. By the time I rebuilt the carb (I did ride it bout 25 miles) now a wheel's already fubar'd and seizing, the frame feels weak, etc.
Not pushing you away from this scene but think what your goals are far out, once I get the bike solid, soon the engine will be an issue again
it'll be a continuously cycle till you've dumped bout a grand most here say they get in their bikes where it runs some what stable. You also need tools to work on a bicycle, engine, etc.
Also whats funny strip it down to single speed, thats what I'm about to do since I can't find a cheap enough rear cassette style rear wheel for the 6 speed, so going to try to just run it like a BMX till I can afford to buy the derailer parts and what not. If your not dead set on a shift kit, if your gears work, why would you switch it?