Need help identifying a mini bike?

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I was driving around town tonight and saw a few people riding these mini bikes around. The frames weren't styled like choppers or street bikes either, which threw me off a bit. It was more of a blend of both, but the loud exhaust definitely sounded more like choppers. They were hitting 45 mph without sounding like they were hitting 7000 rpms so I would assume it was a 110-125cc or under. I caught a yamaha logo on the seat, but couldn't find anything on Yamaha's website that looked remotely close. Any insight, pocket bike/pit bike/mini chopper riders?