To properly balance out a steam system the air valves are critical and not just a hit and miss application.
To properly install these valves use the smallest orifice radiator closest to the boiler
then increase the size as you get further away.
By doing this your equalizing the amount of air leaving the system so all the rads heat about the same time.
You should also check your main vents as for operation as you want the air out of the mains as fast as possible and DO NOT use cheap valves Try Hoffman of Equal
http://www.masterplumbers.com/plumbing/plumbviews/1999/steam_heating.html : PlumbViews >> MasterPlumbers.com – The Largest Plumbing Resource on the Internet