Had the same problem yesterday, thought it was the solenoid, which also holds the bowl to the carb.
But it was just the start of my problems, the float and needle valve assy was broken too, so gas was leaking into the intake and sump. To check I removed the vacuum pipe on the block side of the carb and could see gas leaking through.
I did give it a thorough clean, it was sparkling and checked the float needle to make sure it was sealing, by blowing air though it when it was shut. But somehow it still leaked, may be a sinking float..
In the end just ordered a replacement carb with a newer nikki style, as it seems to happen a lot to the walbro.
Check to see if gas is leaking though the carb, into the oil by removing the crankcase suction pipe.