yes it is an F model with black.
does that make much of a difference?
Welcome!
I have a 78 CB750F (super sport) too.
The major differences in the F (super sport) with the black engine are:
Larger valves which need a different stem angle to accomadate the larger openings. Typicaly people on here say that the later (77' & 78') F's experience premature Valve guide wear because of the different stem angle. Which can result in smoking out the exhaust during start up and in extreme cases smoking through-out. If you suspect anything do a compression test and if you can, a leakdown test too.
The other Notable differences are Comstar wheels, dual front disc brakes, rear disc brake, different seat with longer tail or fairing, longer gas tank with a lower and narrower profile and of course the nice black finnish on the engine.
The K models dont have any of these.
I lucked out on mine too; I got it for $700 and the guy delivered it to my garage free of charge.
I would get carb rebuild kits first off. As you will read on this site, make triple sure that you clean the slow jets out perfectly, and get a new accelerator pump diaphragm. You may also benifit from getting a new accel pump actuating spring. (the one on the outside of the carb on the linkage. Mine was old and didnt accuate the plunger fast enough. 50 cent @ ace hardware and $30 from the dealer. You decide.
Make sure you can see a steady stream from the pump jets like a squirt gun.
Make sure you are getting a clean fast flow of fuel from the tank too. Check the petcock and screen for clogging and your gas filler cap too. Me and Tiny Robot spent hours in my garage trying to get my bike to start and it turned out it was a clogged fuel line that you could see fuel in, but it wasent flowing like it should have been. I about pulled all my hair out that night!
I have a factory manual in a PDF i can email you if you need it.
Have fun!!
Cheers!
Jeremy