Random fuel leaks (float issues)

I've got an 82 750 four cyl with the Keihin CV34 carbs. Every once in a while one of the carbs will start dumping fuel into the airbox with the engine off. These carbs don't have overflow drains in the bowls. It is very random when this happens, but seems to be more prevalent when the night temperature is low and the day temp is hot. It seems like the float valve just opens up for no reason. Currently, carb #2 is stuck open.

The engine runs great throughout the entire rpm range. The carbs are spotless inside. I rebuilt them a few months ago. New but aftermarket float valves. Float height set to factory specs. Dynojet stage 1 kit.

Anyone else experience this problem or have any ideas what's causing it? The only thing I can think of is debris getting trapped in the float valve seat, but I don't know why it only seems to do it when there is a large ambient temp differential. I do not have an inline fuel filter, just the factory strainer on the petcock.

A properly functioning vacuum petcock should disallow fuel flow in both ON and RES positions when the engine is not running.

In any event, would check for gasoline intrusion into the crankcase, because the oil may now be diluted with gasoline.

Good Fortune!

I have verified correct operation of the petcock. Once the float bowl is emptied, the fuel leak stops. Even if the petcock was stuck open, the float valves should not allow an overflow of the bowl, correct?

Patton wrote: In any event, would check for gasoline intrusion into the crankcase, because the oil may now be diluted with gasoline.

This happened the last time it did this. I changed the oil promptly. At $10 a quart for oil, this problem is going o get expensive if it keeps happening!