I've adjusted my 270 while running... at proper idle there just isn't that much oil to throw around. By the time its at the rocker shaft its basically just flowing... little pressure other than the arms themselves.
Speed up the motor and the fan causes more oil to fly than the rockers.
I guess fr $20 you could get an old cover off ebay or a swap meet and cut the top off... but still... its just not that big an issue.
