[mike721]

I'd be careful with is using 100% water if your in a cold climate, it will freeze and break something, it will get you home in a pinch but if it's cold out you better stop on the way and buy some antifreeze and put it in before you let the bike cool down. Long term just water might cause some corrosion or lack of water pump lubrication issues too, so I'd go with a 50/50 mix.
Side note.. has anyone noticed that automotive antifreeze is now sold 50/50 pre diluted, but the price is the same as it was when it was the concentrate? That's some mighty expensive water in there....

It also helps with some bikes to fill the system, then rock the bike back and forth to free up bubbles. Almost every engine has some nook or cranny that's hard to fill, and some have lots of 'em!

As far as the coolant, every bike manual I have read -- and that's maybe a dozen -- specifies 50/50 water/ethylene glycol antifreeze. Several are specific enough to state never use only water or only antifreeze, but I am sure in a contingency where you lacked one or the other you wouldn't hurt anything short-term. 100% of either is better than not enough!