Those are pneumatic caps. That is for an air line. It probably rides like total shit with that on there. When your suspension compresses, the only thing that actually is compressed is the spring, and the air above the oil in the fork tube. The height of the oil, the weight of the oil, and the number and size of holes in the damping rod determine what your damping and ride compliance is like. With no compressable airspace on top of the fork, you are pretty much running spring only. The compliance of the ride can be dictated by the height the oil is run at, which meters at the same time, the amount of air that is available to compress. Back in the 80's some manufacturers toyed with the idea of using compressed air as an adjustable function, so that when you wanted a nice plush cushy ride you could leave it as delivered, but when you wanted to go out on a "sporting" ride, and maybe wanted it to behave better under heavy braking and cornering loads, you would add as much as 12 PSI to the top of the forks, which effectively lowered the amount of travel required to start forcing the fork oil through the metered orifices (the holes in the damper tubes), so the damping curve was "raised". Some of these setups had a seperate shcrader valve on each fork, but those were near suicidal, as my dad can tell you from hitting a bump at 90MPH on his GS1000. Other, later systems had a single service point, and a "bridge line" that went from the side with the service valve over to the other side, so the chambers remained balanced. This was a superior setup, but people found it cumbersome to mess with, and that "technology" was a bit beyond the average street rider. People would often over-pressurize the forks, and would end up blowing thier seals. Not much pressure was required. Bottom line, get some different caps.
