Motorcycle Repair: Honda sl125 Carb, overflow tube, honda sl125

Question
Hi Bill, I have a 1971 sl125 and I replaced the carb. with a after market carb . It ran great for a couple months . Then it started to leak gas . Not just from the overflow tube on the bottom , but from the little breather tube on the side just above the adjustment screws . This happens when the bike is started and running . What would cause this to happen . Thanks Andy

Answer
Andrew, check to be sure that the brass tube in the float bowl is open and clear to allow gas to overflow out of it. It also serves as a vent/breather to help balance the fuel pressures inside and outside the carburetor body.

The small tube at the top of the float chamber in the carb body is a bowl vent, which also keeps the pressure balances evened out.

It sounds like perhaps the overflow tube in the bowl is blocked and the float valve is leaking or not shutting off, allowing the fuel level to rise excessively and then be pushed out of the upper bowl vent tube.

Pull the carb and clean all passages for fuel and air, including those in the carburator's inlet throat. The two air inlets there are for emulsion of the idle and main jet metering circuits.

Check the float valve to see that it is shutting off and you don't have issues with the float hitting the edges of the bowl gasket. Today's fuels cause a lot of rubber carb parts to swell up causing problems with leaks and also with contacting the floats, as well.

The stock float level for an SL125 is 24mm. If you have an exact copy, then the specification should be the same. If you changed brands to a Mikuni or the a/m copy is from China, then it is hard to say what they specified for a setting. I am not a fan of the Chinese-made carb copies.

Bill Silver