Prime position?

I'm wondering, does the prime position on the vaccum petcock open up the reserve section too so that it drains that section of the tank?
I have my petcock connected to the #2 vaccum tap and it has started to run lean on that cylinder. If I take the hose off and put a cap on the port it runs better. I'm thinking of just keeping the cap on until my winter service and was wondering if prime does open the reserve section too. Any one know for sure?
Thanks,
Ride Safe

I'm pretty sure that the prime will completely drain the tank, not 100% though. Also, unless the tap is busted, your leak must be coming from the vacuum line, which shouldn't cost more than a couple of bucks, and can probably be found at any local auto parts store.
aj

Yes in prime position fuel is being drawn from the reserve tube on the petcock.

If it's running lean on that cylinder, then that hose you're using to the petcock, may have a tear in it causing a vacuum leak. Capping #2 and running on PRI cures it? That should be your indication. Inspect that hose for any cracks, and replace it with a new one. Can't be more than 15 cents for the length you need. If you have this vacuum leak from that hose, your vacuum diaphragm in the petcock might not be opening completely, losing the battle against the diaphragm spring.

The only way I know to drain the tank completely, is to turn it upside down.