low end bog is pretty common and tough to find. Could be a low idle, dirty clutch, worn belt, carbs, etc.
I would start by balancing the carbs. If one side opens before the other, it bogs down.
Clean out the clutch, spray it down inside where the weights are with carb cleaner. They are supposed to be dry (no lubricant in there) and clean the surfaces where the belt rides (also should be dry)
Set the idle to where it is just below where the clutch moves in to grab the belt.
The manual written in the 80's was for oil that was not as thick as it is nowdays. The new oil used for injection does a much better job than it used to. the idea behind using premix and injector is to make sure there are no air bubbles in the lines. but it makes them run poorly.
** the manual says to run premix at 25:1 for the first 3 gal of gas (not 40:1)of Kawasaki oil My guess is Kawi oil is probably diluted for better mixing with gas **
Glad you got it going!!
Trucker, you beat me to this post! you are still the Kawi Guru!!