Let me lead off with a bit of advice. While you can get digital versions of the shop and repair manuals – and you should totally get all of them – the book that fellow SOHC4 forum member HondaMan (Mark Paris) wrote (My CB750 Book) is equally indispensable. Yes, it is pricey but get it. It’s hard to describe the value of the book until you read it, but it is like a conversation with a gifted Honda tech (which HondaMan obviously is) where the why, where, and how is explained in such a way that you yourself feel like you might just be able to reach that level of technical ability when working on your bike.
Link:
http://forums.sohc4.net/index.php?topic=65293.0Secondly, another forum member Dino did an excellent video series of him rebuilding a ’73 CB750 and goes into great detail AND gets good shots of the work so you can see what he’s talking about. I highly recommend his videos as reference material.
Link:
https://www.youtube.com/watch?v=MkHJuU01-WkBackstorySometime in the summer of ’71 and fresh off a divorce, my father purchased a Honda CB750 in sweet, sweet Candy Gold
as one does. Since his buddies at the time all had those slow Harleys and that was the style, he dressed it up with some crazy handlebars, 4” over forks, a Sportster seat, a sissy bar, and lowering blocks to give it that 70’s chopper look.
As a kid growing up, I don’t remember a time when the 750 wasn’t lurking somewhere in plain sight. It was always kept under something shady, whether it was in my father’s apartment, in the garage, or on a covered deck. I remember my first and only “don’t tell mom!” event when I burned my leg on the exhaust after it ran for a bit to clear out the cobwebs. A few years after that, my dad and I rode it south a couple hours to visit family, which helped me fall in love with it.
36 years and 15K miles later, it made its way into my possession when my father passed. It largely sat, neglected but protected from the elements, for 15 more years until recently when I could be around it without getting sidetracked by ancient history. It is still weird to think of it as “my” bike, but it is and if I’m going to ride it (because they deserve to be rode!), then some of the 70’s needs to come off.
This thread is to document that process, some of which I’ll recap.
DesignAlong with the reluctance to call it mine came the desire to keep it just like it was when I got it. That meant unbaffled megaphones, those ridiculous handlebars that pressed the controls into my armpits, the sissy bar, and the skewed chopper-like angle thanks to the longer forks and shorter rear end.
"Sans sissy bar, but with Sportster king/queen seat. Kiddo's face blurred to save her the embarrassment of those bars"Occasionally I would swim through pictures of this era’s bikes looking at rat-style cafes and hard-tail conversions thinking they were a good compromise between the styles I liked and the style the bike was already in. Looking back, they were all pretty bad.
Riding with the lowering blocks and the Sportster seat on it is generously described as “f*****g torture” for my lower back and unbaffled exhaust moves me to tears but is impossible to ride with without ear protection. Seeing as how I’m no longer an invulnerable twenty-something, things had to be changed. This is around the time when I saw a couple of really tasteful restomods like Rawhide’s “Golden Goose” that got me thinking about a cleaned-up stock look and the Universe seemingly shoving stock parts in my face for cheap.
Chopper was out. Restomod stock was in.
The Work So FarLanguishing in the heat of the garage and without frequent flushing of gas, there was some light surface rust in the tank. While I had a spare tank, I wanted to keep the original Candy Gold tank with its minor imperfections so I soaked it for about a week with some grocery store grade white vinegar rather than using a Kreem kit and got really good results. YMMV: I checked in on it daily and I'd suggest you'd do the same if you try this.
By this time some of the easier, cosmetic things that could be done got knocked out right away. The sissy bar was off and in the attic. The Sportster seat was on a shelf thanks to a sweetheart deal on a K1/K2 seat (with no tears!) The baffles are now (mercifully) rewrapped and reinstalled. Oil was changed. The battery was replaced. New tires were put on. However, the forks were still too long, and I had yet to realize there were lowering blocks that needed to come off.
Design-wise, I had made some progress but mechanically I had done very little. I remembered the seemingly only issue my father frequently battled (or complained about) – the front brake and jumped right into rebuilding the master cylinder and getting the caliper to both brake and release. This was an encouragingly easy project. Fluid was drained, new seals, new fluids, and time spent cleaning out cavities and cleaning up parts. Up until recently it was a trouble-free unit – it is now a bit of a squeaker/whiner.
That win under my belt I decided to jump into more issues. My around-the-neighborhood test rides indicated I had a blown fork seal so I purchased a new pair and started in on the replacement.
"Yuck"Draining the existing fork oil is just like everyone describes it – how does fork oil end up smelling that bad? (Hint: the seals leak water) I used a 3 ton floor jack as a counterweight and attached the forks to it like it was the axle and pulled the tubes out. Looking back, you should place some cardboard or something impact absorbing that won’t scratch where the fork lowers will inevitably land. I did not – which meant more work cleaning them up.
This was about the time that I realized my forks/cushions were not the same style as everyone else’s and I couldn’t use a spacer to lower my forks down because the K1’s don’t have dampers like the like the later models.
"No rebound spring - the fork spring rides on the shoulder of this damper - which isn't supposed to be removed, btw"The springs seemed to be in good shape and I avoided the temptation of just removing the 3.75” spacer and instead put them back together as I had found them. I used a piece of PVC as a slide hammer to move the seals down into position while installing the tubes into the fork lowers, reinstalled the snap ring, lubed the tubes lightly, and put them back on the bike while I searched out replacement tubes. For fork oil I used 10w30 because temporary.
New fork seals now sealing, it was time to address that the bike ran like a turd. It wouldn’t idle but it would happily cruise along at speed. Considering the years of neglect, I figured a carb cleanout and rebuild was in order, so I ordered new parts and began scrubbing down the carbs with carb cleaner and a brass brush. Afterwards they looked great, but I likely damaged the brass overflow straws/tubes on three of the four float bowls and those are hard to find.
"Carbs ready to be disassembled and parts kept together. Seriously, watch Dino's videos on carbs"
"So much cleaner. Not perfect, but not gross"
"One of the three brass overflow tubes I broke during cleaning. These can be FRAGILE"Testing the tubes for leaks is fairly easy:
- Pull the carb bowl off the carb
- Connect a low powered air supply (less than 5lbs – you’re just going for enough to hear or feel air movement) to the rubber or plastic overflow hoses at the bottom of the bowl
- Plug the tiny hole at the end of the brass overflow tube – you shouldn’t continue to feel or hear air. If you do, feel around for the source and you’ll discover your crack / leak
If you have leaks they can be repaired by soldering them closed or possibly by placing a tight-fitting, fuel safe hose over the brass tube (leaving the head of the tube exposed.) I tried neither of these solutions as I had enough complete carburetors to build out two more bikes and just grabbed bowls to replace my damaged ones. There’s nothing wrong with part hoarding if you can keep it out of sight of folks who would complain, right?
With the float bowls no longer dumping gas out, it was time to set the float levels and since putting the carbs on and taking them off the bike to do this is a PITA, I took inspiration from another SOHC.net user who set up his carbs and tank something like this:
"Old overflow lines support the bottle while lightly secured via zipties. Original Sportster seat and that left-side cover that's always f*****g broke also pictured"With the carbs bench synchronized and back on it was time to do a running vacuum sync. Oh, and setting the idle. No one talks about how that is achieved on the K1 models with the GP-style rack and throttle assembly. All the references I could find talked of a mythical idle screw that was very much not installed on mine. Looking at the carbs while I had them out to clean them, I feel that it’s an adjustment of the slides along with the air mixture screw. If I’m wrong, please point that out, but I have an around 1K RPM idle and it accelerates smoothly though with somewhat of a razor-like curve.
"Vacuum Synch!"At this time, I decided the drag bars I had on the bike were too low and that the superbike style would look a little better and allow me some more room around the massive stock master cylinder to push the forks up through the triple-tree so that I could bring the front end down a bit. This was a good time to also replace the aging and still very lengthy throttle and clutch cables. I ran the electrical through the bars and the new bars allowed me to bring the master cylinder up a good amount allowing an inch of fork to be pushed up through the clamps, which I’ve read is just about as much as you want to push through before you run into clearance issues. The lowering blocks were pulled off the rear shocks adjusted up to the high settings to accommodate my chunk.
"From this: Drag bars"
"To this: Superbike bars"Not a huge change, but better ergos for sure.
I installed my new-to-me stock seat after sourcing some hinges of the bay of E’s and used hinge pins from interior door hinges to attach it. I still need to cut them down to length and drill a hole to accept a cotter pin so that they don’t go anyway during thievery, but for my current use just the pins are fine.
Update: Jul 30My out of round rear tire is actually a bent rim. The folks at the shop I got the tire from were super cool about it and showed me exactly where the bend is and proved it wasn't the tire. Oh well might see about trying to pound that out over the winter seeing as how it isn't a super bad dent.
New standard length fork tubes have arrived!
"Now to find time to install them!"When it isn't 100° in my garage, I'll be getting the new tubes mounted up. I'm really looking forward to a somewhat regular stance (and these improved riding characteristics I keep hearing about)
Update: Aug 30: The new forks are finally on!
"Looks a million times better without those stilts up front!"After letting the dang things sit for a month, I finally lucked out enough to get some weather where the heat index wasn't on par with swimming in lava. I do recommend taking pictures as you go, because it's good for documenting the process for knowledge sharing and just in case you forget if you put it together right. Pictures beat the heck out of tearing something back down just to see it's right.
After pulling the forks off I started breaking them down. After getting the snap ring off, which is its own special hell without the correct tool (which I refuse to buy for some reason), I have found that my floor jack's front axle and my K1's front axle are similar enough sizes that I can bolt the fork up to the floor jack to make pulling the tube out of the lower cushion super easy.
![](https://i.imgur.com/VQB4VSV.jpg<br />[size=8pt]"Semi-securly attached to the floor jack axle."[/size]<br /><br />[img width=450 height=600]https://i.imgur.com/AN4gOPI.jpg)
"Flip the floor jack and the fork upright, stand on the floor jack, and pull up sharply on the fork tube. Be prepared to catch the lower cushion or have something soft for it to land on."After getting the fork tube out, it was a simple matter of transferring the parts from the old to new tube. Here are some pictures just in case you're curious of what goes where
"The two smallest snap rings go just above and below the holes here."
"This ring goes on with the beveled end facing away from the bottom of the tube (towards the top nut)."
Like so! Obviously, you'll need to install one of the smallest snap rings after this goes in place since they hold it in this location."
"Next comes the larger machined sleeve with the beveled inside edge towards the previous ring and the two smallest snap rings."
"Mine was a little damaged with rust on one of the forks due to a perpetually bad fork seal. I lightly sanded the rough spots and rust off and then thoroughly cleaned it before installing. A little bit of fork oil is handy for making the installation a little easier as well as pre-lubricating both the tube and the sleeve to aid in protecting them."
"Next comes the largest snap ring that holds the sleeve in place. This installs to the very bottom-most edge of the tube."
"Like so!"
"Next comes the middle sized smap ring. It installs in this location (the top-most snap ring location relative to the true top of the fork.)"
"Like so!"
"Finally, reinstall the top hat. It is positioned with the ledge towards the top-most side of the fork relative to the true top of the fork. Your fork seal rides on top of this ledge."
"Like so!"After adding some fork oil and letting the bike warm up while I cleaned up the whackload of tools and broken nitrile gloves, I took it out for a little jaunt through the neighborhood and it feels so much more stable than before. I'd say I should have done this earlier, but I support my avoidance of the heat.
Currently
"It is super easy to take good pictures of this bike"Currently, the bike is running fairly well, though has some issues getting up to and around 80mph. I suspect I have some clutch adjustment issues from my cable installation and likely adjusted it incorrectly. It does run strong, though doesn’t like pulling off the throttle suddenly and will die. I am doing a lot of night driving, so I’m not sure if this is a combination of old wiring and the stock headlight bulb, but it’s on my list of things to look at.
I’m enjoying some night rides here and there because it’s kicking around 100 degrees during the day here and because I’m still trying to get used to riding versus driving and the less combatants I have to deal with on the road the better. I will say, there is a lot less oil leaking from the bike now that it is being ridden. There’s something about these machines. They don’t want to be a decoration - they just want to run.
Still To Do- Do the accumulated maintenances up to 15,000 miles to make sure they’re done
- If I’m going to do some more extensive summer riding, upping the oil weight a little
- During the winter I want to strip everything off the frame and get it cleaned up and repainted. Since the motor will be out, I’m planning on repainting it too though I’m not sold yet on stock silver or black for the jugs.
- I need to replace the current brake line because it’s about 8” too long
- LED or H4 headlight conversion
- LED taillight bulb
- Replace the wiring harness
- Add in some HondaMan suggested relays
- Add in HondaMan’s electronic ignition gizmo
- Possibly respray the tank and side covers, though to be honest, they don’t look terrible. Candy Gold is available but LOL at the price. I might go with House of Kolor Aztec Sonoma Gold (HOK1221-03)
- New exhaust because those megaphones are not doing it for me. I thought about cutting them down to just before the rear axle (removing the cone at the end), but I can’t bring myself to do it
- Adding period correct looking turn signals with LED bulbs
- Replacing the clutch side control so that I can make use of said turn signals
