Took my ninja out for a spin, it felt like the back end of the bike was swaying from side to side. Didn't feel confident at all, checked out some forums that said inflating the tires would probably help, which I did but it only helped marginally. I'm wondering if it's something mechanical or suspension related that's causing the poor ride quality. Appreciate your comments below ...

Video -->
Bike: Kawasaki Ninja 250R
Original Tires: IRC Road Winner
New Tires: Pirelli Sport Demon

 

The sprocket should not be loose! Man, that's scary. The chain looks about right, it is stiff side to side.

 

The cush drives on all of the kawi's kinda suck. They get hard and cause some throttle response jerk when rolling on the throttle. But you did not move the sprocket in the proper way to initiate that issue in the video it seems.

Stock tires suck
Good move with the sport demons for the street or light track days.
Set up your suspension the best as possible. Good chance that you will be swapping out springs and such for the 180 lb ish people out there.

Welcome to KF

 

@Briensiac: Guy at the shop said the cush bumpers are kind of worn but not worth replacing right now.

@Dagone#19: Thanks! I'm 165, you think it's worth swapping out springs?

Update:
Don't know where this metal thing fits on the rear axle, or which side it should be oriented! Took a look at the service manual but I couldn't identify the part from the diagrams.