® No overflow system

Keihin, the maker of all of Honda's and most of Kawasaki's carburetors, has in some models done something pretty strange. On many of these carburetors there is to be found no overflow system. Examples are all Honda V4s, most if not all of the VD, VP and later carburetor families, all Gold Wings (including the Valkyrie) and such Kawasaki models as the ZG1000 and the Kawasaki models related to it. Also many Mikuni-equipped Yamahas and Suzukis.

By an overflow system I mean a way for fuel above normal design level to become evident externally. To be seen. Most carburetors and most Keihin carburetors have such a system. It's simply a brass standpipe inside the float bowl that diverts to the outside fuel that somehow reaches excessive height. Just as the standpipe in a toilet diverts excessively high tank water straight into the plumbing.

On a bike without an overflow system, when the carbs overflow--and this is not such an unusual event--there is no telltale, no visual clue. Two things result from this. One, it means overflow can happen, whether from dirt around the float valve, a blocked bowl vent, or an issue with the float itself, and you never know it. There is no sign. Not good, I think. Because the second thing is, this fuel is going to go somewhere and not onto the ground where it is visible and can serve as a warning. Instead, it will flow into the engine. The fuel enters the engine and eventually makes its way into the crankcase, where it dilutes the engine oil.

On the Gold Wing, the fuel often also backs up inside the air plenum, puddling there and then when dry new layers puddle over it again, and those drying also, eventually there is formed a surprisingly thick layer of hard, almost epoxy-hard varnish. This is what causes Gold Wing throttle shafts to become twisted.

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