Topic: The CB750 HP thieves, over the years...

[Don R]

Very informative, thanks. My June of 75 build 76F came with the rear disc and the 18" rear tire.

[Bill/BentON Racing]

  I'm sure I've got some old mag tests,will look! Bill

[74750k4]

Some very good info in here, despite the bickering. I plan on taking the best of both early/late/aftermarket guides, valves, cam etc., and create what Honda never got to do. It won't be stock, but it might look like it!

[Wobbly]

Some of the F1 had rear disk brakes: not all, though.

All F-Models had a rear disc brake.

The later K7 sometimes came in black, and the K8 was mixed black and silver versions.

Only the F2 and F3 models came with black engines. The K-Models never did.

The valve guides of the post-1975 F and K engines are very short-lived

After 36 years and 210,000 miles, I finally replaced them. Short-lived? Not so sure.

[HondaMan]

Some of the F1 had rear disk brakes: not all, though.

All F-Models had a rear disc brake.

The later K7 sometimes came in black, and the K8 was mixed black and silver versions.

Only the F2 and F3 models came with black engines. The K-Models never did.

The valve guides of the post-1975 F and K engines are very short-lived

After 36 years and 210,000 miles, I finally replaced them. Short-lived? Not so sure.

Uh-oh, old fight back to life?

Wobbly: there's a beautiful, original 1975 F0 in my neck of the woods, perfectly preserved and recently brought back to the world of the 'riding' folks. It has no rear disc, and his dad was the original owner. It still has the original Candy Red color, in great condition! Build date is 2/75.

Last year I finished building a cafe' K7 bike that was owned by the original owner until he backed his pickup truck into it in 2008, after which it sat next to his garage in the weather until [this new owner] talked him out of it. It has a factory-black engine (now 836cc). Build date is 1/77.

Honda did many things like this in the day: my K2 is one of the first 800 K2 bikes imported to the US. It has a 100% K1 engine.

Your exceptional valve guide life is like O'freen's bike: he has an early F and it has over 140k miles on it with no special oil-burning issues. My own K1 head had Stellite guides in it with no valve seals, with the guides being just like the K0 guides, extra long. I just replaced them this summer at 140k miles, as they were worn just enough (about .0024") that I didn't think I would get another 150k out of them. Recently I met another fellow here on the forums who has a genuine F0 head with Stellite guides in it, so at some point Honda had gone back to the tougher stuff, at least for a while, after 1974.

This also was Honda's bent in those days: they often made early versions of the models with extra performance, which faded away as production increased. It seemed to have much to do with their intended quality, which suffered a little when their costs got out of hand: this was the explanation given in Sochiro's biography of the time.

[brandEn]

Great post Mark!
It's interesting that there is actually some rear drum brake F0 models out there.

[Tripps]

Just a couple of comments on my 78. I have a bud who is a whiz with carbs, he did a great job of rebuilding them to stock specs, even with a battery too weak to start with the starter, it will start second kick after sitting for months, it may have been 4 or 5 months. Running an average of 75 mph on the highway, I pretty consistently got 49.5-49.9 mpg. It definitely hits a wall in 5th gear, I have never been able to break the 100 mph barrier.

[Jerry Rxman Griffin aka MuthaF'er]

Mark,

I'd love to see the 2/75 F0 you are referring to. By candy red are you referring to the 76 candy antares red color or a different red? Perhaps you can hook us up one day?

How would I determine if my guides are stellite?

I totally agree about that sometime extra performance. CB750 K0 Super Sport #1606 ran like a scalded ass monkey until I dropped that valve. 

[Retro Rocket]

There were lots of differences between different markets as well, blinkers, colors, handlebars, gauges and plenty of other little idiosyncrasies.....  Nothing surprises me any more....  Actually, it won't be hard to prove the F model with the rear drum because it should not have the rear master cylinder bracket and should still have the longer F frame, I would like to see that too...

[Vreihenmotor6]

I have never heard about an F0 with a non disc rear

I rebuilt my 75 F with a 17 tooth sprocket which i believe to be the proper size (backed up by Honda parts lists) , not the 18 listed on the previous pages, just FYI

[BobbyR]

Just a couple of comments on my 78. I have a bud who is a whiz with carbs, he did a great job of rebuilding them to stock specs, even with a battery too weak to start with the starter, it will start second kick after sitting for months, it may have been 4 or 5 months. Running an average of 75 mph on the highway, I pretty consistently got 49.5-49.9 mpg. It definitely hits a wall in 5th gear, I have never been able to break the 100 mph barrier.

I suggest you go over the bike and carbs again. My 78 pulls like hell in 5th. You should be able to pull 100 easily. I do have 120 mains which may help that. Measured mile speed in a Magazine test was 123mph. Beat the Kawi by 2 mph.

[HondaMan]

Just a couple of comments on my 78. I have a bud who is a whiz with carbs, he did a great job of rebuilding them to stock specs, even with a battery too weak to start with the starter, it will start second kick after sitting for months, it may have been 4 or 5 months. Running an average of 75 mph on the highway, I pretty consistently got 49.5-49.9 mpg. It definitely hits a wall in 5th gear, I have never been able to break the 100 mph barrier.

There's a clue in your MPG: those are the EPA- "approved" carbs. There's 2 things you can do that will improve the top end, while slightly dropping the MPG (and making the top end last much longer: increase the mainjets about 3% to 5%. If you increase the jets just 3%, then raise the float level by 1mm. If you go with the 5%, you may be able to leave the floats where they are but still reach to 110 MPH if traffic [patrols] will let you?

Some of the CA carbs have as small as #100  mainjets in the K7/8 engines. Those suffer REAL short exhaust guide life, and often burned valve faces as well.

[HondaMan]

Mark,

I'd love to see the 2/75 F0 you are referring to. By candy red are you referring to the 76 candy antares red color or a different red? Perhaps you can hook us up one day?

How would I determine if my guides are stellite?

I totally agree about that sometime extra performance. CB750 K0 Super Sport #1606 ran like a scalded ass monkey until I dropped that valve. 

Yep, it's the Antares Red. He just had me make a long-wire Ignition to hide in his tail trunk. I hope to see the bike one day: so far he has only sent me pix, which is what got the conversations started. He thought it was a 'hybrid' of some kind because of the rear non-disc, but I have now seen 2 of them. One was the bike I rebuilt for a serviceman while he was deployed 4th time to Iraq, had it a year. It had a GL1000 front end on it with dual discs, and a drum rear, and a gorgeous 'balloon' muffler with a tiny ding at the back that he put in when unloading the bike at my house one frigid December night.   A shop in Ohio where he lived had installed an incorrect (K4) clutch cover on the engine because it was nicer than the original one, and the clutch lifter spacing difference broke his hub. I got it first to fix the clutch, then had it a year when he was suddenly re-deployed with no warning, poor guy!

Build date was 3/75 on the steering neck. I don't know when the rear drum/disc thing settled to the disc. By this time the Old Factory was not making the 750 anymore, so the variations can't be 'blamed' on that situation. I suspect that it was just Honda doing it the way they usually did, as the K5 "died" from their production in 1975. I am supposing the leftover rear drums then got 'dispersed' into the F0 bikes. Then, at U.S. dealer's demands, the K6 suddenly got back into the builds again: this is why some of them have "K" top ends and some have "F" top ends, while some have things like "K" top ends with "F" cams, etc. Some K6 bikes also got the close-ratio gearbox, which I have seen just once.

If you see it once, it's like seeing a roach in your house...

[JohnnyM]

Hello,
Picked up a brand new never been opened 900cc Henry Abe piston kit from a friend.  Am in the process of building a motor with it.  Got a mildly hot cam recommended for street riding.  Got the heavy duty cam chain.  Will have my shop do the screws on the cam cover to hold down the cam. Bought the rubber intakes from Sudco to use a set of 29 smooth bores.  Here's the question.  Will the stock connecting rods be OK or should I try to find  set of HD rods?  Do not plan to race or drag race it. (have a Z1 for that)  Just want a hot street bike.  A friend from England knows an old guy who does Aluminum work so I had him build me a set of CR 750 body work.  Tank, seat and oil tank cost me $400 but it took 3 years to get.  (actually ordered the aluminum stuff and waited for it before I even started with the project)  Am using a 74 frame and motor as the basis of the project.  Also any recommendations for things I should do to the motor as well?
Thanks for any advice you can give me. 
Johnny M

[ofreen]

Yep, it's the Antares Red. He just had me make a long-wire Ignition to hide in his tail trunk. I hope to see the bike one day: so far he has only sent me pix, which is what got the conversations started. He thought it was a 'hybrid' of some kind because of the rear non-disc, but I have now seen 2 of them.

Build date was 3/75 on the steering neck. I don't know when the read drum/disc thing settled to the disc.

I'm very skeptical that any production F0s had a drum brake. They were advertised with the disc brake from the get-go, Honda parts books and later fiches never showed anything else. The build date on mine is 2/75. I've never seen an F0 that wasn't orange or blue. 

[Retro Rocket]

Yep, it's the Antares Red. He just had me make a long-wire Ignition to hide in his tail trunk. I hope to see the bike one day: so far he has only sent me pix, which is what got the conversations started. He thought it was a 'hybrid' of some kind because of the rear non-disc, but I have now seen 2 of them.

Build date was 3/75 on the steering neck. I don't know when the read drum/disc thing settled to the disc.

I'm very skeptical that any production F0s had a drum brake. They were advertised with the disc brake from the get-go, Honda parts books and later fiches never showed anything else. The build date on mine is 2/75. I've never seen an F0 that wasn't orange or blue.

Or Yellow or red.......

[ofreen]

I'm talking USA. The '76 F1 was yellow or red.

[Retro Rocket]

The 75 was never referred to as "FO" in Australia, 1975 F1....

[ofreen]

Rear drum brakes on any of them?

[HondaMan]

Hello,
Picked up a brand new never been opened 900cc Henry Abe piston kit from a friend.  Am in the process of building a motor with it.  Got a mildly hot cam recommended for street riding.  Got the heavy duty cam chain.  Will have my shop do the screws on the cam cover to hold down the cam. Bought the rubber intakes from Sudco to use a set of 29 smooth bores.  Here's the question.  Will the stock connecting rods be OK or should I try to find  set of HD rods?  Do not plan to race or drag race it. (have a Z1 for that)  Just want a hot street bike.  A friend from England knows an old guy who does Aluminum work so I had him build me a set of CR 750 body work.  Tank, seat and oil tank cost me $400 but it took 3 years to get.  (actually ordered the aluminum stuff and waited for it before I even started with the project)  Am using a 74 frame and motor as the basis of the project.  Also any recommendations for things I should do to the motor as well?
Thanks for any advice you can give me. 
Johnny M

With 900cc, you must use HD rods, or they will bend, at best. That's just beyond the strength of the stock rods. The old Powroll 836cc 11:1 pistons were enough to bend those stock rods, if run hard. If kept below redline, though, they held up quite well!

[Retro Rocket]

Rear drum brakes on any of them?

Never seen one...

[Bill/BentON Racing]

Curious to also see a F model with drum brake.......was Honda pts mgr, sv mgr, tech and have never seen one,also no bulletins or paperwork showing one or any pic! Mark,please get us a pic of setup. Really interested to see how it was done, thanks, Bill. Thanks again for your book and info!

[HondaMan]

Curious to also see a F model with drum brake.......was Honda pts mgr, sv mgr, tech and have never seen one,also no bulletins or paperwork showing one or any pic! Mark,please get us a pic of setup. Really interested to see how it was done, thanks, Bill. Thanks again for your book and info!

On the one that was here at my house: it had a "regular" 750 swingarm, like the early K models (box section arms). The brake pedal was mounted in the usual "hole" (tube welded to the lower frame), didn't look out of the ordinary from a "K" perspective. But, the plate on the steering neck was definitely an F model, 1975 build. It also had the 530 chain and sprockets, with the oiling hole plugged in the final drive so it would not oil, and a 17T/48T drive sprocket setup (although neither sprocket was OEM).

[MRieck]

It sounds like somebody was swapping parts...either the frame tag or parts. I wonder if the frame # on the left hand side of the neck matched the tag? Magazines received early bikes....I have never heard mention of drum brakes on an F. Personally I've never seen one or heard of one in almost 40 years.
 Mark Haycock's Honda CB750 book talks about a prototype F but the steering head had less rake and the longer swingarm (non K) was employed . This was done to evaluate attempts to make steering more responsive. This didn't work out well ( judged "to sensitive") so a second prototype bike was made with with a rake of 28 degrees (greater than that of the K (27 degrees). The trail was increased to 119mm as compared to the K (95mm). The longer swingarm remained unchanged and that was the final version of the bike. 1975 colors are listed as Flake Sunrise Orange (my bikes original color) and Candy Sapphire Blue. As Ofreen mentioned...Sulphur Yellow and Anatares Red were 1976 colors. Then there are the obvious differences like the external wire connector box and front caliper. Th external box is very noticeable and requires the welded on tab found only on the F frame. Different oil tank etc etc. There are no pics of the 2 "prototype" F bikes.
 The 75 and 76F ran 530 chain...nothing out of the ordinary about that. The F swingarm is box section...just longer with different chain adjusters.
 Considering the bike you saw had a regular k swingarm it sounds like it can't even be one of the 2 prototypes (if they somehow managed to survive which would is very difficult to imagine). It really sounds like somebody was swapping a VIN tag or something. That used to be done on stolen cars all the time "in the day".....nothing new there as it happened to a friend of mine in 1977 and he bought it at a "legitimate' used car lot.
 I would be very interested in seeing engine number on the mystery F.

[HondaMan]

It sounds like somebody was swapping parts...either the frame tag or parts. I wonder if the frame # on the left hand side of the neck matched the tag? Magazines received early bikes....I have never heard mention of drum brakes on an F. Personally I've never seen one or heard of one in almost 40 years.
 Mark Haycock's Honda CB750 book talks about a prototype F but the steering head had less rake and the longer swingarm (non K) was employed . This was done to evaluate attempts to make steering more responsive. This didn't work out well ( judged "to sensitive") so a second prototype bike was made with with a rake of 28 degrees (greater than that of the K (27 degrees). The trail was increased to 119mm as compared to the K (95mm). The longer swingarm remained unchanged and that was the final version of the bike. 1975 colors are listed as Flake Sunrise Orange (my bikes original color) and Candy Sapphire Blue. As Ofreen mentioned...Sulphur Yellow and Anatares Red were 1976 colors. Then there are the obvious differences like the external wire connector box and front caliper. Th external box is very noticeable and requires the welded on tab found only on the F frame. Different oil tank etc etc. There are no pics of the 2 "prototype" F bikes.
 The 75 and 76F ran 530 chain...nothing out of the ordinary about that. The F swingarm is box section...just longer with different chain adjusters.
 Considering the bike you saw had a regular k swingarm it sounds like it can't even be one of the 2 prototypes (if they somehow managed to survive which would is very difficult to imagine). It really sounds like somebody was swapping a VIN tag or something. That used to be done on stolen cars all the time "in the day".....nothing new there as it happened to a friend of mine in 1977 and he bought it at a "legitimate' used car lot.
 I would be very interested in seeing engine number on the mystery F.

I might have a picture of the engine number: I think I took a picture of the clutch on it for the owner when I found the problem (a 'vintage shop' had installed an incorrect clutch cover, in chrome, during a visit just prior to my receiving the bike - the clutch would not work afterward). I'll dig around int the pictures I have from the period (I think this was in 2007?)

The frame # on both sides of the neck did match, and it had the little "wire box" on the front, as I had to replace some corroded bullets in there that had been wet a long time. The bike was here almost a year: the poor owner got sent to Iraq suddenly (4th tour!) the week before he was to come back from Texas to pick it up. Heck, he drove it here in his pickup from Ohio, went back there for his family to move to Texas, and 3 months later got redeployed. I'm in Colorado! Wow....he's tough stuff!