KZ440 Fork Air Pressure?

There are way to many post talking about forks so I will just ask this question specifically for my bike. I have a 1982 KZ440 LTD A3 with the air assist forks. I have read and read but can not find anything referring to the proper amount of air to have in these forks. A guy I know said to put 10-15psi in each fork. I can not find anything in the manual either so do any of you know what the proper air pressure setting is for the forks on the 440 LTD? What is the difference in less pressure as apposed to more pressure...i.e. softer, stiffer? Thanks guys...and gals.