Pics always help. But is almost impossible to do the math with out knowing the RPM. Could spend lots of $ and find out it is 7,800 when you planed for 3600 RPM or versa vice.
What are the numbers and where are they on the engine? #s on the carb will give clues. Not great ones but would narrow things a bit. I have a buddy who is a second generation lawn mower/small engine guy and will ask him if we can't find any thing online.
Don't give up! This is just part of the party that is motorized bicycle riding.
<- you after 1st ride...