vacuum petcock problem

So I have a conundrum with this dang vacuum petcock... it's virtually brand new (maybe only two tanks of fuel through it before I tore the bike down)
Now, it doesn't seem to want to deliver fuel when it's in the "on" position. I have to switch it to prime or else the thing quits feeding my carbs... I wouldn't think that it would need to be rebuilt that quick... what else can I do?

Check the vaccume line for cracks and make sure that it is hooked up correctly. Sounds stupid, but stupid things happen to the smartest people from time to time.

Is it a SUZUKI petcock?