Topic: CB 550 K or F. Which one do I have?

[cjcampo61]

I just bought a 1976 CB 550.  I'm assuming that the engine number identifies it as a "K" or "F" which is a Super Sport I'm told.  What letters or numbers should I be looking for.  Also, was there any differences in the "K" or "F" engine?

[streak09]

Not familiar with the numbers, someone should be along soon with a definite answer, but... The F model had a 4 into 1 exhaust. I believe the F model had a lock on the gas cap? http://www.sohc4.net/cb550-model-guide/ This should give you what youre looking for

[Tews19]

F and K model differences are cosmetic.

Welcome to the site and pics are always welcome. Post a few for dissection.

[geminimotors]

The F bikes VIN on the neck will begin with 550F, In 75-76 the side stand will be directly below the left foot peg, and the passenger pegs will be mounted to triangular tube hoops. The F tank has a flap or door over the gas cap and is a bit longer than the K tank, making the F seat shorter than the K as well. The tool kit on an F is under the rear of the seat, instead of on top of the airbox as on the K. There are other differences in things like the indicator lights, side covers, and things get even weirder for 77, the last year of the 550F.

[Stev-o]

Both had locking fuel tanks with the hinged door over the gas cap, except early K models.
The carbs are different too.

[Bankerdanny]

The 550F models always used a tank with the filler cap under a hinged flap. The 550K models had an external chrome filler through 1976. In '77 the F and K models used the same basic tank, although I believe that the fuel tap's are different, but with different decals and badges.

The F model used the same carb's through its entire run ('77 was the last year for the F). The K got new carbs in '77, so for that one year you can tell the F and K engines apart based on the carb's they have.

So, If it's a '76, the tank style and exhaust that will tell you it's an F. The correct 4-1 F exhaust has all four tubes bent to the brake lever side of the oil filter housing.

[Stev-o]

.....that is if it is still stock and not had parts changed out.  Good info Danny.

[cjcampo61]

Thanks for the replies.  The bike has an aftermarket 4 into 1 exhaust made by LFU.  The original airbox is gone and the carbs have K&N pod filters.  The gas cap is not under a flap on the tank

[Stev-o]

Most likely a K then. How does it run?  With the mods you describe, the carbs would have had to be rejected to run good.

[Tews19]

Curious what LFU stands for... Any pics?