If the tap has a vacuum line

It will not let any fuel through unless the tap is under vacuum

ie- with engine turning over (that is enough vacuum to open the tap) or engine running

Make sure you have vacuum at the hose when you hit the starter button.

Or take the hose of the manifold end, place hose in mouth and suck

with the tap in the on position fuel should flow when sucking. And stop when you stop sucking.

You will not get fuel in mouth

Is the vacuum hose ok  splits etc

is it connected to the manifold properly

always use pingels on bikes i do or own but have seen ppl leave tap on an have cases fill with fuel mainly with s&s carbs only good thing bout standard taps is got a good filter into tank

Hey Z, make sure a wasp hasn't blocked 'm up with mud,lol