Hey DJ, Whats the deal with the "MX" & "YZ" models?. My brother had a 125 that looked identical to the one that T-Red posted a pic of (silver one). Now the Larson Brothers who once owned it always refered to it as the "B", to this day I'm not sure if it was a nickname "Bee" or if it was the model but I think it meant both.
Eventually the poor little things frame broke up badly, fractured tubes around footpeg area & down tubes separated from steering head. Last year while searching thru the families dump in search of TM bones I found the rusting remains of the Yamaha's frame, I was so excited because I could maybe identify what this bike really was but sadly the steering head was missing, so no ID numbers.