Try our new info resource - "Aladdin's Cave" (Main menu)Just added a separate link to Ash's Dropbox thread (shortcut)
That's weird as if the tap internals are as they should be you would have a greater fuel pressure in reserve - lower in normal ON position.Out of interest what happens if you are on reserve and open the filler cap.
The floats and float valves will do their job irrespective of what position the fuel tap is in, the fuel can only pass down through the same delivery pipe. Is there a chance that the tap is actually leaking in that position, and gravity is allowing the fuel to run down the outside of the pipe, running over the outside of the carbs, and following the easiest path downwards which would be via the overflow pipes. Make sure everything is bone dry, kneel down next to the bike, then using a torch,(NOT A MATCH!!), turn on the fuel and see if the outside of the delivery pipe becomes wet and shiny. Have fun, we love this hobby don't we? Late PS:- I meant to say that it really does sound as though the tap has been wrongly assembled. There's an exploded parts diagram on the CMSNL website, might possibly help.
I think I would be looking for a new tap myself by now!