So I finally got around to replacing the impeller in my WH6 I ran it this afternoon for around 20 minutes. Once it was warm it ran beautifully. I brought it up to wide open slowly and ran it there for a few seconds and then backed it down to an idle. Thats when it stalled and wouldnt restart. I noticed that the carb was flooded. I let it sit for about 15 minutes and went out and started it again. Did the same thing and it stalled again. So what is going on?
Do you have the original cork float in the carburetor. If so, it sounds like it may need resealing with clear, fuel proof dope. If the original shellac sealant is gone (gas, especially with ethanol will dissolve it over time), the float won't "float" and it consequently won't do it's job shutting off the fuel flow .... i.e. you end up with a flooded out motor.
Anyway, that would be my guess. Instead of resealing an old cork float, you can also get a replacement plastic float at East Coast Marine (on the Mark 6 page). You don't need to seal those.