I have a 49 cc Chinese quad , when I brought it it started fine I put it away for Xmas n had trouble starting it after , I drained the bowl n put fresh fuel in and got it going we went out n broke pull start so now we use electric start which hardly ever works so I buy a new battery still we have a problem except when it starts its trying to drive off at high revs so I pik the bak wheels off the floor and they just spinning really fast I rev the quad and its cutting out next I've looked in carb and float is ok and freely moving ,I've messed with air screw n can't seem to stop it revving so high pls Hlp!!!!

 

That sounds like a vacuum leak. Check to make sure you didn't knock a rubber line off somewhere. If not grab a can of starting fluid and spray any rubber lines, wher the carb meets the boot, boot to intake (or carb flange if yours doesn't have a boot), intake, and intake to head. If the engine changes revs then you found the leak. Simply disassemble and find out why (bad gasket/o-ring, loose bolt, ect...)