There are several things that could reduce the power that's getting to the ground. The drive belt is the first and easiest thing to check. On the transmission clutch, the belt should sit flush or a little above the clutch faces. Also check how tight the belt is by pushing down on the belt between the engine and trans clutches. It should go down no more than about 2".
Another very common problem with the Kawasaki is running on one cylinder. I have seen a lot of those engines that drop a push rod and therefore doesn't run on that cylinder. Remove the valve covers and see if the pushrods are still on the rockers. If one has fallen off, it's usually easy to fix. First make sure the pushrod is strait and not damaged. Then make sure the valve moves freely before trying to connect the pushrod again. The valves often glue themselves shut after they are not used in an otherwise operating engine. Again they usually free up and work fine after you open/close it by hand. Replace the pushrod and run the engine for a little while. Change the oil after that. I have fixed many Conquests with this issue and the Kawasaki Mule utility vehicle also has this trouble, with the same engine.
Everybody dies, but not everybody lives.