The standard CB ( non super sport) is a K. Super sport is a F, and then there's the C and the LTD.
The C was shaft driven, 10 speed and had it's own unique frame.
The L, or LTD, was a K with special body panels to mark the tenth year anniversary of the CB750.
The only difference I know for a fact between a K and an F frame is that the F has a mounting tab for the rear master cylinder ( disc brakes), whereas the K had none due to being a drum brake rear.
Rumor has it that F frames use tubing with thicker walls, but I've never cut either open to know for sure. However, I am convinced that a bare K frame is noticeably lighter than a bare F frame, so there may be some truth to the myth.
I'm almost positive that you can interchange K and F tanks and seats between the two frames. The mounting points look identical, but I've never tried it myself.
The 1979 frame, the 1980 frame and the 1981-82 frames all used slightly different steering head angles. The general consensus is:
79- kinda lazy, cruiser style steering angle
80- more upright for a sportier handling.
81-83- somewhere between the 79 and the 80.
* This only applies to F frames.
Now, that's only taking about the actual frame. There were other differences between other suspension parts. The F had a different swingarm than a K. Mainly to accommodate the rear disc, but I think it's also slight wider.
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