MHVDM

Hello everybody! I would assume it's not often people come here and ask about Yamaha TZR50 issues. I'm brand new to bikes, this is my first moped I am learning, and I've owned it for about a year now. It has some issues that I want to look into. It has a prebought CDI tune, and I think this CDI has caused some issues for the bike (can't be sure though, I don't have the OEM CDI). The issue is at midrange RPM, the bike struggles getting up in speed, even on flat grounds, it doesn't gain any speed at all and just remains on the same RPM and sputters like it's getting too much or too little fuel. Possibly running too rich? (I have to shift down to get up in speed) How would I check on this, and do someone here have any tips and tricks I could use to check it out? I have tinkered a bit with it, pulled off every piece of the bike and engine that I feel comfortable with (max the carb). So I have tried to learn, but I couldn't figure out why it sputters. I also believe it's getting too much oil, it eats oil like crazy, compared to my other moped. Can this be adjusted too? I can't test drive it sadly, because the chain is too loose and it jumped off during driving one time. You guys here probably have a lot more experience than me, and asking you would probably be the best choice here. Best regards,