That's probably going to be a trial-and error thing for you, based on the combined weight of you and your kart. With everything including the engine in place, tack- weld the mounts on at 45* and have a seat. If they sag more than 50%, you're too soft. If they sag little or none at all, too hard. If too hard, lay them down more. If too soft, move them closer to straight-up-and down. In most cases, ideal is where the kart rides at around half-travel, or slightly less, allowing the most compression and rebound the shocks will allow. This concept is the best for keeping the rubber in contact with the ground.
The actual travel you get out of them depends both on the mounting angle, and the physical distance between the suspension pivot point and the wheel centre, as compared to the shock's actual location between those two points, as allowed by it's own travel. Confused? Sorry. Try this:
A two-inch travel shock mounted straight up-and-down exactly halfway along the suspension arm will itself travel two inches. Thanks to leverage, the wheel will travel FOUR. If that same shock in the same place was mounted on a 45* angle relative to the suspension arc, the wheel would travel eight inches. The catch is that the spring rate will be reduced as the shock unit us moved further away from the wheel AND as it's tipped away from 90* relative to the suspension arm. At this point, the actual math involved is beyond me, but the principal is true. Hence, the tack-and-test approach.
