Yamaha Chappy carburetor tuning issue

#1
Hi everyone, I have a Yamaha Chappy and I was wondering if anyone could tell me how to adjust and tune the carburetor. It has a Mikuni carburetor and I can only find one screw that looks like an adjustment screw. I know this is not exactly a mini bike, more of a moped, but if anyone could help me out I would really appreciate it.
 
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