I wonder if your enrichener circuit (choke) is plugged or disconnected somehow. Haven't heard of anyone having this problem. Try this, with your engine running, pull the choke knob to see if the engine revs up. If it does, the circuit is ok and you have another problem.
Another item you failed to mention. Do you shut off your petcock after you ride? This might be the problem since the fuel in the bowls might be evaporating and on start up the bowls have to refill before starting. Leave the petcock on overnight. See if this helps. If it is the prob, you might have to get into the habit of turning on your petcock and waiting for a minute before starting.
Any other guesses????
