Purchased a 1990 Moto4 80cc for my six year old and spent a few nights getting it running (Battery, carb cleaning).

Started it up last night and it ran solid it did however not return to idle it would run at a high RPM and eventaully idle. I was thinking of just buying a rebuild kit but I don't know it I need it.

Could it just be a cleaning of the throttle body slide? or something else?

 

hows the boot between the carb and engine? spray it with carb cleaner, if engine speeds up or slows down, boot is cracked, sucking air, something is suckin air, like a vacume leak, thats why it wont idle

 

Also make sure the slide is dropping all the way down when throttle is released, even a tiny gap will raise rpms until it falls back down, could be a burr on the slide, a sticky throttle cable (get a cable luber and flush it out) or a bad/weak slide spring. make sure the linkage the throttle hooks up to moves freely and snaps back to close when released. Older carbs usually have a little moisture corroision on the internals that will gum up shafts and linkages and prevent smooth movement.