You don't need a whole new carb, that little feul tappet Fred mentioned wont cost more then $4, a new floater won't be more than $10 and the gasket (IF you need a new one) will be about $2.50. You can also use some liquid gasket instead or (if you're desperate) some rubberpaste. But I still think it's the feultappet-thingy or a leaking floater.
A brandnew carburettor costs no more than $75 , if you want to replace it for an oversize-high-performance carburettor with apropriate inletmanifold $150.
Go to your local Honda mopeddealer, if he doesn't have or can't get a carb for you he doesn't deserve to be the official dealer.