I am new to suspension forks, so be gentle.

By air preload do you mean the air valve on the top of the forks? Yes, I have that. There aren't any other adjustments that I can see, top or bottom.

Boy is this bike dirty. Someone thought that taking a handful of grease and slathering the chain and chainwheels would make the bike run better. I don't know when the last time this thing was cleaned.

Ian