It might be a Yamaha Enduro.
There is a picture of John Oates, of the band Hall & Oates, sitting on a yellow Yamaha motorcycle with Daryl Hall standing next to him. The motorcycle is a 1979 Yamaha DT125 Enduro. Yamaha made 4 different size DT models in 1979: a 100cc, 125cc, 175cc and 250cc. As far as I can tell the 125 and 250 models were both yellow in 1979 and looked very similar, but if you look closely the first half of the exhaust pipe is on the right side of the engine on a 125 model, and on the left side of the engine on the 250 model. That's one way you can tell John Oates is sitting on a 125cc model and not the 250.
The Yamaha DT models were dual sport motorcycles powered by a single cylinder 2 stroke engine. I don't think the term "dual sport" was coined back than, so it was common to call this type of motorcycle "enduro," which means the motorcycle is designed to be ridden on and off the road. This was accomplished with a lighter weight motorcycle, lights and turn signals, longer travel suspension and toned down knobby tires. In 1979 all models except the 100cc model used a single shock rear suspension Yamaha called "monoshock." The Yamaha monoshock rear suspension was first used in 1973 on Yamaha competition motorcycles, but eventually made it's way to other types of motorcycles.
This type of motorcycle was very fun to ride, and the DT models sold very well for Yamaha. It's too bad EPA rules killed 2 stroke powered motorcycles, but I've heard of different technologies for 2 stroke engines that lower emissions, so maybe someday motorcycles like this will come back again.
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John Oates sitting on a 1979 Yamaha DT125 Enduro with Daryl Hall standing next to him
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A 1979 Yamaha DT motorcycle advertisement
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A 1979 Yamaha DT125 Enduro
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A 1979 Yamaha DT250 Enduro
