This advertisement is for the all new (back than), 4 stroke powered 1979 Honda XR250. The ad first appeared in late 1978. I think its an interesting ad because who doesn't like Thumpers, and Honda's claim the XR250 is capable of competing with 2 stroke powered motorcycles. 2 stroke motorcycles dominated the dirt bike market back than because they were fast, light and cheaper to build. Four strokes engine's require more parts making them heavier and more expensive, and giving them characteristics less conducive to dirt bike racing. The XR250 was not a competitive racing motorcycle, at least not out of the box. I don't think any serious dirt bike racing enthusiast from the 70's considered 4 stroke motorcycles a serious threat to 2 stroke technology, but today, four stroke motorcycles dominate dirt bike racing. Its not because the bikes are faster, but I think it has more to do with pollution and noise than anything else.
Motorcycle manufactures like Honda saw the writing on the wall by the mid 1970's. You start to see two stroke powered motorcycles disappear as new EPA regulations are rolled out. I'm not really sure how these new regulations effected dirt bikes, but I do know you don't see many larger displacement 2 stroke motorcycles competing today. The XR250 was not a replacement for fast 2 stroke motorcycles and I don't know why Honda tried to sell it that way.
The XR line of Honda motorcycles were never considered "competitive" in a racing sense, but they were reliable and fun which made them a popular recreational dirt bike, and are still manufactured today.
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