There should be a model and serial number plate or sticker located either on the frame or under the seat. The engine also has a serial number and model on he base of the engine .
3RB-012812 is not a frame number for a 250 Yamaha dirt bike; it's a motor number. To find out the model year and frame, you need the frame number.
the frame
The serial number should be located on the frame,after you open the cylinder.Look where the cylinder arm lays into the frame.
That would be a 2000 model year.
Frame
klf 300-frame number LF300c-604814
Need to know barrel length and ALL markings.
on most it should be somewhere on the frame like on a Honda is in front by the shock
It's on the frame.
Look on the frame and butt.
N frame S&W Model number.