Gas Tank Switchover Valve Problem

[tracker2007]

I have a 50 HP and a new 5 HP, both Mercury's. I had Bass Pro Shop install a mechanical switchover brass valve accessible from the outside so that I can operate both engines off the main tank. Beings I am several miles away from BPS I took it to a local marine mechanic. We pulled the valve off and found no obstructions in the valve; it seemed to be working fine. The 5 HP has a gas line bulb that doesn't seem to fill up with fuel using all three remaining positions on the valve. It has worked off and on but when it begins to malfunction, the bulb needs to be squeezed several times to keep it running. Eventually it dies for lack of fuel. I finally have resorted to carrying extra gas and add to the small .30 gallon capacity tank. I do not like to carry gas on the boat, for sure. The valve has four positions 12,3,6 and 9, all of which have an audible click. The 50 HP runs fine in one of the positions. Any ideas out there?
Any advice or help would be greatly appreciated.

Tracker2007