Somewhere between 5-15 PSI, with 7.0-7.5 PSI being optimal for most folks. You MUST use a low pressure pump, or you will blow the fork seals in less than a heartbeat! It also requires a low-pressure gauge, if you don't have these already, you will need to pick them up -- search the Internet for such. Cheers!
1979 CB750K (sold, 2012, but not forgotten)
1983 Kawasaki 440 LTD Belt Drive (sold, 2011)
1993 Kawasaki Voyager XII