When my '95 CBR1000F Hurricane is on the road, it runs great. However if I leave it over night, or let stand for a few hours, it is hard to start. It fires up on full choke, and runs for a couple of minutes, but soon the revs die and the bike engine stops. When trying to re-start its like the carbies it is either starved of fuel or flooded.
Sometimes I can push it off the centre stand and slam the breaks on - and it will jolt something loose, and the revs come up again.

Could it be a blockage that settles when the bike is still?

 

Maybe the vacuum operated petcock is sticking due to a piece of crud in it. Try pulling the fuel hose and the vacuum hose off the carbies and suck on the vacuum hose with the fuel turned on. You should hear a slight click and fuel should run freely. I'd also drain the tank, take the tap and petcock apart and give them a clean. I got a new diaphragm kit for mine and have had no more probs.