Dew this!!!! I want to do the same.
Got my 14 YO son a Coleman for Christmas. After Christmas I realized it was a blast, and went and got ME a used Axis off marketplace.
We have woods and river bottoms. These damn things will literally go anywhere. They are more fun than they ought to be. His new one was $699 and my used one was $325.
Sure, I know real ATV's would be better, but kind of like OP, my wife doesn't mind the minibikes- doesn't count them as dangerous as 'the real thing' somehow. Also like OP, I like to tinker on things. You can do a lot of tinkering for not much cash on these platforms. And they ride pretty good. Not at all like the classic vintage minibikes most remember.
I want a little more umph out of mine. So far I've got a pipe with tip muffler, open air filter and a re-jetted carb. Removed the throttle stop, but I haven't touched the governor yet. Would like to do the billet flywheel and rod so I can safely get more RPM, but I don't want to lose the headlight as there is no billet flywheel with lighting coils.
We tool around in the evenings after supper. The headlight is kind of critical. I have put an upgraded LED bulb in the stock housing, and now it's pretty bright.
Been planning to do the torque converter mod, but a motorcycle style engine with actual tranny would be amazing.
Do those motorcycle style engines have lighting/charging coils integrated?