Are you saying;
when you turn the valve to Reserve, You get NO fuel from the tank...
It would have to be in the valve... IF the tank has gas...
My 95 sportster, thinking I had the same tank gas valve you have. The only problem I had with it is ONCE , when I syphoned out gas for the mower,,, knocking off the tube that Kept the reserve gas from coming out on the regular valve on position... Yes I ran out...
it MIGHT be a clog in the LOWER part of the valve to tank hole when switched to RESERVE.
I would take off the line there, at the valve (fuel line) and put it on reserve and try a LITTLE compressed air to Blow Back and into the tank... IF you hear bubbling and air is moving in it, may be cleared.
Keep the gas cap OFF when you do this...
That Has to be where the problem is....
If I remember correctly, on my 95 it is two separate holes going into the tank Regular one with a plastic hose to hold gas above and a Lower one to allow gas to flow after the top line ran out and switched to reserve.
I think the Valve only changes DIRECTION from one to the other and OFF.
So blowing it out may be the FIX...
signed....BUBBIE