Just recently my L1 has developed a bizarre starting problem. When I go to start the bike, the starter will endlessly turn over showing no signs of firing. It will continue to do this almost indefinitely, regardless of whether I give it any choke or throttle. If I then switch it off and leave it for a few minutes and then try and start it again, it will fire almost as soon as I press the button and run fine. It will do this any time from a cold start in the morning to a quick stop at the petrol station, and is a bit embarrasing when I cut the engine at level crossings and it won't fire back up again!
It seems as if no fuel is getting through initially rather than flooding, as there is no hint of backfiring and no smell of petrol coming from the exhaust. What I can't figure out is why it will then start fine after being left doing nothing for a few minutes

I will rip the bike to bits to investigate sometime. Aside from checking all the obvious suspects (fuel filter, pump etc) but does anyone have any ideas as to other possible causes I could look into whilst it's in bits?
Thanks in advance.