It's not necessary to drain the coolant to perform a valve service. But some do, and they remove the radiator in order to get some extra "elbow" room so to speak. I suppose it's possible that an air bubble may have formed and the system needs to be purged. Did you check the overflow tank level? If that empties it's possible for the system to take up some air. The level should always be above the MIN line.
I don't recall the O/P saying he removed the radiator cap, and looked at the coolant level in the radiator... would have been my first step...
please elaborate about this so we all can understand, myself included.
I ask this, as this bikes cooling flow path, and parts, while possibly being able to have a bubble form if something was diconnected, would have said bubble purged thru the current designed systems hose from the w/p back up to below the sealing surface of the rad cap. This bike has an 'improved' system, with an actual 'purging hose', that pretty much expells trapped air, directly back up to the radiator top. Unlike the C10, which needed purging either / or from both the w/p bolt, or the bleeder on the thermo housing.
look closely at the cooling sytems diagram, in the FSM, and you will see what I mean.
only air that can 'remain' in the system, after starting and running, will reside at the top of the radiator, right below the cap, and topping that off, and filling the o/f bottle to it's 'fill line' will suffice to effect a full system... so, if the bike is NOT leaking coolant, it really can't suck air into the radiator from an empty reservoir bottle.
sounding to me, like during the valve adjust, the radiator was disconnected and tipped forward, and when reconnected, never refilled correctly, or had the clamps tightened up right.