Thanks for the replies.
Fire Support sells the manuals, but they have none in stock for the Hicap 5.1.
The hop up adjuster is shaped like the bottom half of a circle. I want to disable it, and then turn it on a little at a time to get the best setting. I guess that with the marker on the wheel completely to the left the hop up is off and that turning it to the right activated the hop. There is no way of seeing from the breech if it is on or off and removing the barrel and hop up unit is a tedious job. Even then I found it hard to see the movement of the hop.