There are dozens of versions of the MonoJet so this may help or may simply make it more confusing.
http://www.carburetor-parts.com/asse...ice_manual.pdf
Not plugged, that's a bowl vent. Even with your version of the Vent Valve there should still be a hose nipple.
Have you found the end of the third hose coming from the charcoal canister?
I usually check floats by simply dropping them in a tuna can full of gasoline.
You can test a fuel pump off the engine. I'm not going to tell you it is as good a test as an actual running test with fuel. Mount the pump in a vice and plumb a 0-15 psi gauge to the pump outlet. Operate the pump lever with a vice-grip pliers. It should show 4 - 4 1/2 and the pressure should not drop between strokes. A finger placed over the inlet will show a continuous suction.
This test obviously won't show a leak, but can eliminate a pump with bad valves.
I replaced my 6 cyl pump last Aug. and posted this on an ongoing L6 pump thread.
The old pumps i have pulled off had a tab riveted to the pump arm. I believe it to be a sacrificial metal to prevent wear on the cam, pump lobe. The new Carter pumps don't have the tab. I spent time finding out that Airtex pumps still have the tab. i spent more time and gas getting an Airtex from the Truck Shop. I tested it before installation and found that the pressure dropped between successive pump strokes.
I then bought a Carter from NAPA. It pumped to 4 psi on the first stroke and stayed there on every successive pump cycle.