I want to replace the leaking vacuum style petcock. Your replacement manual petcocks say "must be turned off if the bike sits for more than a few hours". Why is this? Does this carburetor have something that allows the fuel to not be shut off at the floats or something?
In a perfect world the float valve will stop the flow of fuel into the carburetor except for when the carburetor needs more. Most of the time you can get away with forgetting to turn the fuel off, but if the float valve leaks, even just a little, all the fuel in the tank could end up in the engine crankcase mixed with the oil, and/or all over the floor of the garage. That’s bad news for your engine and of course a fire hazard. This is the reason the stock petcock is vacuum operated. It shuts the fuel off for you every time the motor is shut off.