Topic: 'F' Model Designation

[Loudpipe]

Did the 'F' model 750s have different designations like the Ks did? Maybe I'm just thoroughly confused, but I've seen people posting stuff like K5, K8, etc.  If so, how do I figure out which mine is?

Also, what were the differences in the 'F' 750s and 'K' 750s? What about in the F and the F Super Sport?

Thanks in advance. This forum seems to be about the only place I can find information for these bikes.

[Rocking-M]

As I understand it,
75-76 F super sport
77 F2 super sport
78 f3 super sport
this for the SOHC

[Loudpipe]

Thanks, Rocking-M.  Was there a difference in power through the years?

[Rocking-M]

I think the 77f2 and 77f3 had the most power which was pretty close to the
K0's and the K1's. I don't know the exact figures.

[Jerry Rxman Griffin aka MuthaF'er]

1975 CB750F - also referred to as F0 - found in Honda parts fiche as 1975 CB750 K0 Super Sport
1976 CB750F1 - same as 1975 except colors
1977 CB750F2 - bunch of updates including engine with increased HP
1978 CB750F3 - pretty much same as 1977 - may be some minor engine differences - HP should be same as  the 1977F2

F & F1 probably closest HP to 1969 K. F2 & F3 probably highest HP.

Any of you F2/F3 chime in if my info is incorrect on your bikes

Jerry

 

[Rushoid]

The F3 goes to eleven. Just in case you need that extra push over the cliff. 

[6pkrunner]

The F3 goes to eleven. Just in case you need that extra push over the cliff. 

Nigel Tufnel I presume?

[Rushoid]

 

The sustain, listen to it.
I don't hear anything.
Well you would though, if it were playing.

[JP]

Here is my knowledge, and I am about 95% positive about it, so here goes:

RxmanGriff is close to 100% on his post, I am just confirming most of it.

Basically, if it is an F, it is also a SS, so there's that.  The big difference between the years is with the black motors.  If it has a black motor, then it is an F2 motor (unless someone has re painted it).  This is the performance key.  As I understand it, there was no F3.  In both 77 and 78 they where labeled F2 - I have a 78 F2, nowhere does it say F3 on it, maybe this is due to an early production model, but I think the F3's where DOHC models in 79.  I could be wrong here, but if there is a true F3 SOHC, then there is little or no difference between it and the F2.

The F2 engines where THOUROUGHLY different than all other SOHC 750's.  So different if fact, that many of the engine covers are not inner changable.  F2 heads and cylinders Must be used together due to a difference in the way the oil drains from the head. 

The valves on the F2 are much bigger than the K's and the Clutch basket allows an extra clutch plate.  These are the biggest difference and are responsible for the extra power, along with different gear ratio's.

The F2 is capable of around 100HP without getting into the bottom end, with typical mods such as bore, port and polish, electronic ignition, cam, and carbs.  I do not believe any of the K's could achieve anywhere near this without very in depth mods

JP

[Rocking-M]

Interesting JP. Can just the cam be changed for a hp increase in the f2?

Or, say a valve job with cam change, what kinda hp increase could be expected?

Thanks

[eldar]

The later K engines are similar to the f2/3 though. The valves in the f3 are larger however.

[mick750F]

   The US version of the "F" in '78 was an F3. They are practically identical to the '77F2. I believe the '77 carbs still had the clip adjustable jet needle. The '78 needs to be shimmed with washers if you want to change the height. The '78 also had a plug added to the breather system. Both changes to make the bikes more clean air compliant...no changing the carb settings(yeah right) and controlling the release of fumes. There may be another small difference but I can' think of it right now. The '78 is listed as an F3 in both the general CB750 Honda Shop Manual that I have and in the year specific '78 Honda Shop Manual.

Mike

[Jerry Rxman Griffin aka MuthaF'er]

The later K engines are similar to the f2/3 though. The valves in the f3 are larger however.

The K7 & K8 are more similar to the F0 & F1. The K8 vs K7 went with different hardware on the head but both had same size valves and same head as F0 & F1. Carbs changed after 1976 on F & K models.

On a side note here, my info is based on US bikes. The F designation had differences in other parts of the globe apparently like the 1978 750F3 (1978 US model).  Another example for instance, CBen750F1 lists his bike as a 1977 F1 model in OZ. The appearance and color would make his bike a 1976 F1 in the states. It hadn't had all the other updates that they did to the 1977F2 model in the states. I would be interested in hearing from others that have "similar differences".

Jerry

[JP]

Rocking-M,

I am totally just shooting from the hip here, as my F2 is still dissasembled and has never ran since I purchased it with a ceased engine, butttt.......

The right cam and port job should yield terrific results (Assuming you can also dial in your carbs correctly) considering the potential of these engines.  My guess, and I do mean guess, would be around 75 ponies to the ground as long as everything is set up properly.  SOOOOOO many builders are just that, builders.  A Tuner will make an engine perform.  What would most likely happen is a cam is purchased and a generic port and polish job is done, then the carbs will go up about three jet sizes, and then that's it.  You will have flat spots in you curve and you will see minimal gains.  But if you can make it all work together, I think mid to high 70's are achievable.

I am not one to throw around HP numbers and I can't stand it when people throw out guesses about power, but I think what I have mentioned is achievable. 

The biggest mistake I always see is number counting.  I HATE it when people buy performance parts that have a "rating" of x amount of HP and they just count them up and consider it gospel.

Another big mistake is thinking you will see big gains in power by just big boring your engine.  Typically, you just rev slower and have a little more bottom end.  The key to making power is to make everything work together.

JP

Also, I believe the 78 K's had nearly identical bottom ends to the F2-3's.  The only real difference was in the top end.

[Rocking-M]

Hey thanks JP. I may hunt for a cam soon. Maybe not for this winters project though.
I have to many irons in the fire.

[eldar]

I think the head was close to, as for as oil galleys and such. The valves were different though but the K8 does not suffer the F valve weakness. The K8 also has stronger springs like the F3 does. Of course the F is a bit faster but I dont think by too much really. PLus, being a K, I think parts are easier to come accross as well as performance parts.