I'm 6'0 190lbs, I rode my 87 XR200 up until a few months ago. The engine was totally stock, but I put on an XR's Only pipe, jetting, UNI airfilter, airbox snorkel off, and went to a 48 tooth sprocket on the rear (one up from the stock 47 tooth rear). The pipe and jetting helped greatly on throttle response and the gearing helped to keep the little engine screaming away, even with my weight. The lower gearing allows you to use the 6 speed tranny to it's fullest. I ride in soft sand, and had to rev to the moon in 2nd, and still couldn't pull 3rd. After the gearing change, I could pull up to 4th and 5th easily. I never had a problem climbing hills, but after the gearing change, the bike would climb anything and had tons of torque.
With stock motor and gearing you will have to keep the RPM's up to have any power. Clutch won't help you much. Thottle control is the key. Good luck.