Petcock not functioning properly

[loment11]

I have on one occasion forgotten to rotate the petcock from 3 o'clock (PRI) to 6 o'clock and rode for miles without it running out of fuel... I was under the impression that if it is in the PRI position that it is OFF. Is it possible that it isn't working? I don't see an leaking anywhere, which is a relief, but is this strange? Should I be worried about this?
What are people's thoughts about manually closing the petcock upon parking or storing the bike? Is is necessary or just a good idea?
Also, while on the subject, is my dash fuel gauge measuring the entire tank or just down to the top of the reserve?

[SqDancerLynn1]

First IN prime fuel will flow ALL the time. ON & Reserve are controled by the engine vacuum when you turn the engine off the petcock turns off
You should NEVER leave the petcock on prime

[loment11]

Wow, I wasn't aware of that. OK. So, I was used to OFF being in the PRI position... I won't be making that mistake again. All Prime does is bypass the vacuum, eh? So for cold starts after storage, etc. and then swivel it back to ON when it is running?
What happens if you drive it on PRIME like I did after storing it for a few days. How would I end up with fuel in my crankcase? Thanks, LK

[DaveDanger]

IF.. by chance you had a float needle in the carb(s) that wasn't shutting off 100% when parked, the constant gravity pressure of the fuel against the float needle would allow the fuel to slowly overflow the float bowl and into the cylinders and through the rings and on down into the case. Presto.. diluted oil and possibly damaged bearings next crank and runup. Like you determined, the "PRIME" position is to allow the float bowls to fill up after the engine hasn't run in a long time, then switched to "ON" for normal operation. And yes, the vacuum operation of the petcock valve does shut it off when the engine isn't running, assuming the vacuum diaphragm isn't bad inside the petcock. If that diaphragm has pinholes, you have yet another instant path for gasoline to siphon down into the carb, into the cylinder, through the rings... blah, blah, blah. You get the picture

[duaneage]

Another danger is with the fuel lever in pri should a fuel line start to leak it is going to run everywhere when you not home. You also won't have a reserve function and might run out of gas if your not paying attention to the odometer.