It runs nice, I would lower the idle a little bit, and maybe go richer on a high speed needle one or two hours. Be careful when running on grass, it's a lot of resistance and engine can overheat
It sounds like it has multiple issues.
First I will never recommend for anyone to buy used Nitro rc as a first nitro.
Second, it sounds like clutch spring is weak. And it catches at lower rpm. New clutch and spring is 7.29 part number TRA4146.
Second, I would highly recommend 20 percent...