In the 1960's there was a fight among Japanese motorcycle manufactures for a bigger market share. Honda had the 4-stroke engine and Yamaha, Suzuki and Kawasaki were all 2-stroke engines. To get a bigger and bigger market share each manufacturer made more powerful machines that the consumers wanted. To make the engines more powerful, the engine displacement got bigger and bigger. As the engines got bigger, they generated more heat. For the 4-stroke engines, this wasn't a big problem as they could circulate oil to cool the engine. For the 2-strokes, there was no circulating oil, only the air blowing over the fins on the engine. For a while, the 2-strokes got bigger and bigger but eventually the cooling problems couldn't be solved and Kawasaki, Suzuki and Yamaha all switched to 4-stroke engines.
The 2-strokes also had another cooling mechanism and that was to spray oil into the gasoline/air mixture that was burned in the engine. This makes the 2-strokes more of an environmentally "unfriendly" machine. This is why local governments would like these old motorcycles off the street. These older machines are still running in Taiwan, doing lots of good work.
The big fins on the top of the engine marks them as 2-strokes.
There are 125cc with one exhaust pipe but later models have dual exhausts.
The biggest version I've seen in Taiwan is a 250cc, which is probably 2 125cc cylinders side by side. The finning on top is getting bigger and bigger.
In Ballard, Washington I saw what must be the end of the dinosaur line of big 2-strokes. Now the fins on top are getting massive.
But for the size needed in Taiwan, the 125cc is just fine, and the owners are keeping them up. This one just got a new seat.
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