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From Dr Dick of the XLFrum:
An original XR is like the original greenback. Who ever had it used it and now it's no longer in original condition even though it's “the original”. Breaking out REAL info on old race bikes isn't easy. Take the term, original. It's a term that applies to street models, and not racers. Race bikes, by their service requirements, are useless as delivered and therefore obsolete on delivery. When you're talking XR750s, they were not raced in an IROC situation (eg- they got modded to beat the guys who lined up next to you). So an original frame is kinda like the original homerun record or the original land speed record. The original record is zero. When you have a racer you need to learn the heritage (time line) of the sport at time of machine retirement. Then you self-educate on the who, what, when, and most importantly the why your piece of history is in the dress it's in. That takes place of the street bike “factory original” mind set and mile post. from what i can piece together it appears that lots of stuff on the 72's was made to factory drawings by outside vendors. then the factory did the assm. I THINK: bike came in the std HD crate with handle bars removed. Not sure if this was just the 72's or if the 75's were also assmed. It seems that the 77's and 80's could be bought complete but unassmed. After that, HD stopped selling complete bikes and directed you to outside suppliers (for all except the motor). All thru the run, outside vendors were contracted for making new OE stuff. There is a print (right) of one of the frames. ²⁾

New redeigned 750cc engine with aluminum cylinders and heads. Also had new valves, pistons, rods, flywheel assm, “E” cams, carbs and tuned exhaust, 7/8“ dia handlebars with an aluminum ball end clutch lever and a fiberglass seat/fender with a foam cushion.

• Engine Type: OHV V-Twin
• Carburetion: Dual 36mm Mikuni carburetors and specially designed air filters
• Exhaust System: Tuned duals with reverse-cone megaphones
• Bore and Stroke: 3.125” x 2.983“
• Displacement: 45cu, 750cc
• Compression Ratio: 10:1
• Max RPM: 8000
• Clutch Type: Multi-plate dry clutch
• Primary Drive: 25 tooth engine sprocket, 59 tooth clutch, triple row roller chain
• Rear Drive: 16 tooth transmission sprocket, 40 tooth rear wheel sprocket
• Overall Drive Ratio: 5.90:1
• Transmission: Constant Mesh, 4 speed
• Transmission Gear Ratios:
  • 1st 2.09:1
  • 2nd 1.51:1
  • 3rd 1.14:1
  • 4th 1:1
• Weight: 295 lbs
• Tires (front and rear): 4.0 x 19 on aluminum rims
• Front Forks: Ceriani with 4.40” travel and aluminum fork bracket
• Rear Shocks: Girling hydraulic racing shocks
• Gas Tank: Fiberglass construction with 2-1/2 gallon capacity
• Oil Tank: 3 quarts
• Electrical: Fairbanks-Morse magneto
• Color: Jet Fire Orange