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Difference between revisions of "Harley-Davidson XR750"
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==A Very Special Harley== | ==A Very Special Harley== | ||
The Harley XR appeared in 1970 as a replacement for the aging side-valve 750cc KR. Its new engine was still a traditional [[V-twin]] | The Harley XR appeared in 1970 as a replacement for the aging side-valve 750cc KR. Its new engine was still a traditional [[V-twin]] | ||
but this time the bore/stroke ratio was oversquare. Quadruple camshafts in the crankcase controlled the overhead valves, giving tuners the widest possible range of latitude in engine timing. | but this time the bore/stroke ratio was [[oversquare]]. Quadruple camshafts in the crankcase controlled the overhead valves, giving tuners the widest possible range of latitude in engine timing. | ||
==An American Art Form== | ==An American Art Form== | ||
These machines only developed 73 horsepower at 7600 rpm and their cast-iron heads, derived from those of the [[Harley-Davidson XL1200|Sportster]], posed serious cooling problems. Harley was back on target in 1972 with a second version fitted with aluminum heads. It delivered 87 hp at 7800 rpm and could easily top 100 hp when race prepared with such items as electronic ignition and [[Mikuni]] [[Carburetor|carburetors]]. The secret of Harley's domination of dirt track racing is the suitability of the XR, the torque of its V-twin engine,the wide choice of gear sets and the extraordinary way it gets the power down on to the track. Studded tires are banned on the oval dirt tracks and, at over 110 mph, riders depend on their mastery of the art of broad sliding. | These machines only developed 73 horsepower at 7600 rpm and their cast-iron heads, derived from those of the [[Harley-Davidson XL1200|Sportster]], posed serious cooling problems. Harley was back on target in 1972 with a second version fitted with aluminum heads. It delivered 87 hp at 7800 rpm and could easily top 100 hp when race prepared with such items as electronic ignition and [[Mikuni]] [[Carburetor|carburetors]]. The secret of Harley's domination of dirt track racing is the suitability of the XR, the torque of its V-twin engine,the wide choice of gear sets and the extraordinary way it gets the power down on to the track. Studded tires are banned on the oval dirt tracks and, at over 110 mph, riders depend on their mastery of the art of broad sliding. | ||