I have an early 60s c100 and I'm almost positive that they shift the same. Starting in neutral, hit the back pedal on the left side of your bike to go to first, 1 up (the front pedal) is back to neutral, up again is second, up again is third. 1 back from there is second, back again to neutral. I think your stalling the bike from shifting too early, let first wind out longer than you would expect and stay in first up steep hills. The pedal on the right side of your bike is the back brake, Hope this helps.
P.S. if you ever want to sell it let me know