I have to admit...I am not intimately familiar with the physics of the carb, hence my questions here. And I believe what you're saying, Ranger Ron...but I just can't see how there wouldn't
be a siphon effect once fuel is flowing. Completely disregarding the carb for a moment...Fuel flows down through the fuel valve during normal operation via gravity; any time this sort of thing happens, a siphon effect can occur. So if I switched from the "on" to "reserve" quickly enough, there'd still be fuel flowing down through the fuel valve and creating the siphon that could draw from the hose. I could imagine I wouldn't want to start the bike from this reserve hose unless it was last shutdown from it as well.
All my thoughts aside, I'm giving it a try on the bike tomorrow. I have some faith it might
work and I don't have much to lose. It worked for one guy, or so he wrote online
And he ran the hose inside his tank to the right side so it had the center "hump" to pull fuel over.
Tonight I cut down the valve's main brass tube to 1" and connected and run the Tygon as I outlined above then installed the valve on the tank [this means "reserve" and "on" are now switched assuming this works]. No leaks so far. The worse that'll happen is that the new reserve won't draw any fuel but I'll still be able to draw from the new main unless the hose is somehow obstructing flow. If that's the case, I'll ditch the reserve hose soon enough and put a taller tube back on the valve to more or less return it to how it was.