Vintage Dirt Bike Q & A

I purchased a parts bike for spares for my 1973 CR250, now sold the bike and want to sell the parts bike. The parts bike is a 1976 MR250, I was told same bottom end as CR250 1973-1976, is this correct? All the other parts look to be exactly the same as my CR250, so I will be listing on e-bay, wheels, forks, carb etc. Are the other parts the same from the MR to CR, I want to list on e-bay honestly.

The 76 MR250 motor will interchange with 75 and 76 CR250 motors. The 73-74 CR250 does not share as many parts with an MR250. In 75 and 76 the CR250 used an up pipe design moving the exhaust to the other side of the frame. The cylinder bolts to the cases not through the head like the 73-74 CR250. The clutch cover, ignition cover, shift shaft and some other small parts interchange from 73 through 76. The motor design changed from 74 to 75 even though they look similiar the cases and cylinders are not interchangeable.

The carbs may look the same, but they are different. The MR uses a smaller main jet, bolsterd by a third "power jet." The front wheels are different, as the MR has narrower, offset hub for speedometer hookup. Pipes, look the same, but are slightly different--although they are interchangeble in a pinch. Muffler is more restrictive on MR, but will bolt on. Seat is longer on MR, with metal base. Obvious differences are transmission gearing, flywheel/stator, points. The top of the airbox is different on a CR. Frame is carbon steel on MR and chromoly on CR. Fenders are same mold, but white on MR and red on CR. Footpegs are higher on MR and I prefer them for trail riding. Rear brake pedal is different. The only difference on the engine case is one is stamped MR and the other CR (unless they're replacement cases and I don't believe they are stamped). About the only parts that are really exactly the same are: forks, crankshaft, rod, piston, clutch parts, side covers, cylinder head, shocks, shifter, kickstarter, kickstart internal parts, air intake boot and carburetor insulator mount, air cleaner cage, grips, brake and clutch handles, clutch and throttle cable, clutch actuator, brakes, and rear wheel.
Just list the stuff from the MR as from an MR. I'd like to think most buyers know what they are looking for and what is interchangable, but judging from the number of people I've heard from that purchased MT parts thinking they would bolt onto a CR or MR, I guess that's not really the case.

Wow, thanks for all the help and the quick reply s, great knowledgeable people here! I'll list the items accordingly and thanks again .

Mag cover from 73-74 is flat, and will not fit on a MR250, as it's cover has a "bump" on it, to clear flywheel bolt. I think you guys have covered everything else!

I screwed up about the forks. The right lower fork housing is different: MR has bolt locations for speedometer cable holder. Other than that, 75-76 CR forks are same as MR. 73-74 CR forks are different as they have the bolts on top of the springs rather than the circlips.