It still works as an On/Off/Reserve petcock after removing the diaphram to turn the vacuum line into a fuel line. When I take my fuel tank off to work on the bike I just turn the petcock off just like I did before I modified it.
Remember that when the petcock is in it's original configuration the vacuum actuated part of the petcock is only there to stop fuel flow under this single condition: Petcock set to
On or
Reserve and the engine isn't running (so there's no engine vacuum pull to suck the petcock diaphram to its "open" position).
And, of course, the other side of the coin is: the vacuum diaphram can only start/allow fuel to flow if the petcock is set to On or Reserve
and vacuum pull is present in the petcock vacuum line.
So in both its original configuation and the vacuum-line-to-fuel-line modified configuration the petcock's
Off position simply shuts off all flow before it reaches the petcock's vacuum diaphram chamber.
