A 20oz flywheel weight is quite a lot. I think around 12oz is more usual for aftermarket weights. Flywheel weights make a lot of sense on the trail.
But yes, it's a whole nuther world compared to an XR200. On any four stroke, the power at the rear wheel has a much more linear relationship to the throttle and revs. On a two stroke you've got a "powerband" in the rev range where the the engine's power output suddenly jumps. Learning to work with this non-linear delivery takes practice and very careful use of the throttle and gearbox, but can be very rewarding when you master it. All that extra power comes in very handy if the rider can learn to control wheelspin.
An XR200 is probably one of the gentlest bikes on the trails, and you can give it heaps of throttle nearly all the time and not have to worry. The trade-off is that it feels slow and boring to experienced riders (even though in good hands, it wouldn't be far behind because speed is about far more than power). If you think the KDX feels crazy, try riding just about any other serious two stroke out there. It's all part of the fun for us. Long live the smokers!
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91 KDX200SR (240)
85 Virago 1000
http://www.copperleife.com/craig/bikes/