ke 100 low power

I have a 1980 KE 100. Runs great, but low power. I if going up the slightest hill, it will bog down shifting from first to second. At 175 pounds, I may be heavier than the optimal size for this bike, but I still think it should pull me up most hills.

Has anyone else found similar performance issues and have any suggestions? I am guessing that it may be running lean in the main jet.