Motorcycle Repair: overflowing carburetor, twin carbs, yamaha 250cc

Question
blessings,
sir gud day
i would like to ask why my motorcycle carburetor is overflowing.my motorcycle is a yamaha 250cc 2 stroke engine with twin carbs.
i just parked my motor after use with no problems on the carbs.then when i started it again one of the carbs overflows , gasoline coming out of the overflow tube. the other carb is ok.
please help me with this problem. any suggestions will be higly appreciated.

thanks

Answer
Emmanuel,
Yes, those tubes are called overflow tubes and they are there to dirert the excess amount of fuel away from the carburators and to the ground when the float bowls are filled past there correct level. It's only there as a safety measure so that if for some reason the bowl fills up to much, it doesn't start pumping liquid gas into the combustion chamber. A carburator needs a proper level of fuel in it to feed the vetruri sufficiantly so the air mixture passing through the barrel does not be come to lean.
Two things can make excess fuel constantly pour out of the hoses. 1) Your "float level" is incorrect. The floats, like a float in a toilet tank, stop the fuel from entering the carb from the tank when they reach the right hieght. Either they need to be adjusted or one of them has developed a leak and let it fill up with fuel so that it just sits at the bottom of the bowl therby letting a constant flow of fuel in. 2) the other possibility it thet the "needle valve" is stuck open and is again letting fuel enter non-stop. The floats are suppossed to push the valve up into it's seat when they rise from the fuel. Sometimes they get debris around them or varnish up with old dried fuel and get stuck either open or closed.
This job should run no more than $100 at a good bike shop. If you plan to attempt it yourself, purchase a "Haynes" service manual for about $25 and read it closley. Here is some basic info on this procedure I've given others:

Disassemble, clean all jets and orifaces with solvent and COMPRESSED AIR ONLY, use NO wire or picks to clean holes/airways. Rebuild carbs with new gaskets and make sure your floats are set correctly. . Do not overlook the float level, be very sure you are not starving for fuel. In relation make sure fuel flow is unobstructed and use a good in-line fuel filter from the tank to the carb. Even tiny particles in the fuel can get logged in critical areas and cause havoc.

Mike