I have an early 1990's model yamaha moto 4 300 (2 wheel drive). It is leaking fuel from the overflow hose at the bottom of the carburetor. It just started doing this. I have noticed for a long time the choke wont turn off after i have pushed it back down but it eventually idles down. Anyone know what might be causing the fuel leakage problem. Thanks

It can be caused by a dirty carb, either from sitting unused or just a one off occurrence of foreign material getting in there.
the float can become saturated brittle or broken and not floating also a possibility but less probable . usually its just gummed up .

Yes take it apart and clean all jets and replace plastic parts too. You should see some very ugly stuff that accumulates in there. Gas only takes a couple weeks before it starts the varnish process. Run the machine at least every month to keep fresh stuff in the carb.