The number four leaked enough fuel while you were at work to hydrolock or was there petcock problems also? I always thought (hoped) you would need both carburetor and petcock failure to cause a hydrolock condition.
If I read correctly, sounds to me like you could also have an electrical problem, with the starter not working and then starting right up. Battery voltage rising when the starter switch engaged.
Let us know and my hats off to you for tackling that project!
I havent checked the old petcock but will and I will post my findings. Definitely an electrical problem somewhere. Possibly the starter switch or fuse connections. Not sure which as I cleaned both.
I have a few questions. Did you take engine out or do it with it in the frame ? Have you replaced the cover set or a new petcock. And if so did you check it after ? Have you replaced the float needles and springs ? Have you installed a DanMarc ? YOU DONT WANT TO GO THRU THIS AGAIN.

Removed engine. No way can it be done with engine in frame. When I got the bike the petcock was leaking so I installed a new cover set. Several months later it hydrolocked. I rode the bike daily. I will replace the petcock with a new OEM petcock(grab the popcorn folks and let the entertainment begin...lol). The new petcock WILL be tested before installation. New float needles have been
installed and I will vacuum test all carbs before reinstallation. When I got the bike a friend and I cleaned the carbs because the bike had been sitting up and would not run. I wished to rebuild the carbs at that time but was talked out of it. LESSON LEARNED!!! No DanMarc will be installed(see above popcorn remark...lol).
I'm off to bleed clutch and change timing belts. Then the fun starts with carb install and reconnecting pesky airbox, hoses and electrical. Refill fluids and perhaps in a week or so I will get to hit the starter button...and yes , I will be holding my breath....lol