Petcock Vacuum Line

When I got my 82 ltd it did not have a vacuum line running to the petcock . Bike must have the wrong petcock installed bc there is no way to connect a vacuum line to the nipple bc it is obstructed by the engine. So on my carbs the inner 2 are capped and the outer 2 have the standard vent or air lines attached to them. Took me a minute to figure this out when I first got the bike. Actually took few days haha. Previous owner must have been treating it like a gravity fed petcock. So when I run the bike, I turned it to prime and when I park the bike I turn it on (on is like off is how I think of it). Any harm in doing this besides getting the nasty stuff from the bottom of the tank constantly (I have inline filter) or in a crash, the gas would continue to flow possibly being a fire hazard. I hear biggest issue is forgetting to turn back to on and if floats are stuck gas flows constantly and out of the carbs into the engine wrecking things. Thoughts? Rather not have buy a new petcock if I’m not hurting anything with current method. Been running it this way for a few thousand miles with no “known” issue. Should I cap the vacuum nipple on the petcock or ok for it to stay exposed? In pic it comes out right behind “res” kinda hard see

That's pretty silly. That petcock must have been tampered with in its life. You can take the petcock of and unscrew the portion that has the vacuum nipple and rotate it 180 degrees to use it. Otherwise, I have had no problem with just switching from prime to on/res without the nipple capped. 

Also, all four carbs have a vacuum port. They are different from the vents and overflow tubes. Typically, the vacuum ports on number one and four are connected to the Kawasaki Clean Air System that injects clean air into the exhaust ports. The vacuum port on number three is capped and number two is connected to the petcock.
If a port is left open to the atmosphere, that cylinder's fuel mixture will be wildly lean.