This is a Z400 carb. What is the purpose of the stem that comes from the bottom of the float bowl and has some type of external set screw? I just performed some cleaning and noticed a small amount of gas coming out of that tube at the bottom of the bowl case.

Pic of Z400 carb See arrow at bottom

 

It expels fuel if you flood the carb.... helps to keep the bowl consistent with fuel levels.

 

You can also dump all the fuel from the bowl if you're storing the ATV for seasonal storage. Just unscrew the set screw in either case (flooding or storage)

 

Thanks! This forum is awesome.

 

The tube serves a couple of functions. Its the vent, as the hole is open to the rubber tube which hangs down. Its also the over flow, if the float needle valve stays open, or you stand the quad on the rack, itll allow the excess gas to spill out, and on the ground, rather than let the gas spill into the motor. The 'set screw' wont close off either of those functions, they are always supposed to be open.
And at the base of that tube, is a drain, which is controlled by that 'set screw', which allows for easy draining of the carb, for storage.
Picture 6 in my gallery (camera icon on left), shows the carb float bowl and the brass tube sticking up. You can even see the little well, at the bottom of the bowl, where the debrie collects, and where the drain hole is.