Your fun is just beginning! A motorized bicycle requires more frequent maintenance than a pedal powered bicycle. Soon you will be a coaster brake master builder.
Don't forget to clean and lube the front wheel bearings too.
The crank and neck bearings need love as well, just not as frequent as the wheel bearings.
As for your idling issues: remove the air cleaner and remove the idle speed adjusting screw. Look down the throat of the carburetor while twisting and releasing the throttle. You should see and hear the carburetor slide hit the bottom of the carburetor throat. I am a bit leery of the JB weld repair you had to to throttle and you might have throttle cable problems preventing the carburetor slide from closing completely.
The only other thing that may be causing a high idle speed is an intake leak or a horrible crankshaft seal leak. I do not recommend on inspecting the crankshaft seals yet though. That is digging in deep and sorta putting the cart in front of the horse so to speak.
FYI an excellent bicycle maintenance site is Sheldon Brown's (RIP) site:
Sheldon Brown-Bicycle Technical Information
He was a guru on darned near all things bicycle related and then some.