From leaky petcock to carbs, past the float needles ,into the cyls, past the rings into the crankcase. Maybe I'm wrong but this has HYDROLOCK written all over it. I hope not because you might kiss the engine goodbye.
My opinion on petcocks is put it on RUN and never ever touch it again!!! Well,I did use reserve once or twice in 18 yrs. Changed it last week 'cause it seemed like a good idea.