I have a 1980 Suzuki GS 850 and I am having a problem where the rpms spike when I really get on the throttle. If I slowly accelerate there is no problem, everything runs smoothly. When I'm on the interstate and I hit the throttle hard the bike pulls until I get into the upper third or so of the tach range. Then the bike revs up to red line almost instantly. While this is happening the bike itself looses power and stops accelerating. Once I let go of the throttle and slow down to a lower rpm range everything is fine again. Any ideas what could cause this?