It's stamped '73cc' at the base of the cylinder, so I think its the YG5T 80cc. I think they made those through '68. At least according to this article: ridermagazine.com/2014/08/06/retrospective-yamaha-yg-t-trailmaster-80-1964-1969/ and this www.2040-motos.com/Yamaha/Other/yamaha-yg5t-80cc-trailmaster-1968-model-electric-start-dual-sprocket-99245/
Problem is this is a YL-2, Trailmaster 100….
It's stamped '73cc' at the base of the cylinder, so I think its the YG5T 80cc. I think they made those through '68. At least according to this article: ridermagazine.com/2014/08/06/retrospective-yamaha-yg-t-trailmaster-80-1964-1969/ and this www.2040-motos.com/Yamaha/Other/yamaha-yg5t-80cc-trailmaster-1968-model-electric-start-dual-sprocket-99245/