Great idea, I'm going to check my engine in the same way: Just went to start the bike and it locked, the engine didn't turn over, it 'knocked' hard as soon as I touched the starter, so I removed the plugs and turned it over. I small amount of fuel fired out of no. 1, the others were dry. I replaced the plugs and started it up and its running perfectly...thinking I was lucky!
The annoying thing is that I've got lots of experience with vac taps, going back to my 1980's Z650's. I checked the diaphram on this bike and it had a pin-hole in, so I replaced it using genuine K parts...and it started to leak!
The tank was on reserve, I tilted over the tank and sure enough, fuel is dripping through, about a drop every few seconds... just enough to start filling No 1. After having it running on a rigged up tank, all seems well, so I dropped it onto the sidestand, as I need to replace the balance shaft seal. lots of fuel poured out of the airbox!
I think I was pretty lucky today: the bike has been a winter project and I was going to take in for the annual MOT today, another day or two and it would have been much worse. Now I'm just about to order a petcock.