Question edited for clarity.
Question moved from Honda to Jonway.
Buy parts for the scooter you have. Trying to guess parts from other models and makes it fraught with danger and disappointment.
https://www.google.com/search?q=Jonway+Master+2+Parts
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I put in your scooter on google and added how to rebuild came across a manuel see if that helps .There are some sites you can ask on as well that have worked on the same bike .
you got it for next to nothing because the fault was known to the owner
most scooter engines run out of "puff" at around that speed if the crank shaft seals are not in good condition and I am guessing that the owner knew that and was not prepared to pay the repair costs
check the plug as well and if it shows signs of the enter electrode burning away , that is running too lean from the seal problem