i have 1998 kawasaki kx 250cc and would like to know why is my bike leaking fuel from the carburettor overflow?

I have a 1998 kawasaki kx 250cc, i would like to ask some helpful person out there, i have to keep taking the petrol out of my tank by removing the tank, as my bike doesn't get out very much with me having a bad shoulder injury 4 years ago but i still need to start the bike every so often to keep it maintained and running (every 5/6 months) which then leaves the fuel dead, recently when i did this, i washed out the carburettor with some fresh fuel but when i put the tank back on the bike and turned the fuel on at the tank it wouldn't stop running out of the overflow pipe at the bottom of the carburettor, could you please let me know whats causing this, also i would love to know is there any other easier way of me keeping my bike right without having to keep going back to it all the time, taking the tank off, refilling it with fresh fuel, getting a new spark plug, cleaning the carburettor out etc and then hoping the bike will run ok, i'm now doing this for the past 4 years since my injury because the bike means so much to me (good memories), i was working at the bike today but failed to get it started, could be a bad spark, so i'll go and get a new plug tomorrow morning, if anyone out there that could help me with this, i would be so thankful, please god there's a better way of doing this, without so much work involved and not known if the bike's going to start anyway, please could someone share me some know how on this, yours sincerely Sean, thank you for taking the time out to read this, cheers.