Looks like on an R1 there is a 3/16 bleeder hose that is supposed to go to a barb located on the thermostat housing. Most people block this off. If the barb is still on putting a hose on it and taking it back up to the top rad tank you will bleed air from the cooling system on the fly>>handy to have sometimes if you get rushed for time. The prime spot for trapped air is the water pump.
Honest Dad himself
