Topic: 1979 CB650 Build

[Spence_Ellis]

I'm starting a new build thread here since this project has changed quite a bit and the old title is now pretty misleading.
After riding motorcycles all throughout college and in the years after, a long move and new baby left me with a 1979 CB650 that needed a lot of work and no time or energy to do it, not to mention the lack of enthusiasm from my partner. So I sold it, moved, and was bike less for close to 3 years.

During a trip to Vietnam just before Covid, my partner and I went on some great scooter adventures and she was reminded how fun they could be, so we agreed to get a motorcycle when we got back to Canada. Before we had even left the country I had already set up a trailer rental and a meeting with a guy with a 1979 CB650.

It looked great from the outside, but didn't run, and was in classic project motorcycle state. The carbs had just been rebuilt, but leaked, the petcock leaked, the battery was dead, and beyond that I had no idea, but for $900 seemed like a good deal. I put together a list of parts from 4 into 1 and began assembling a kit of parts to rebuild all the things I knew I would want updated.

It is almost road worthy now, but I'll run through the whole process in case anyone else is out there working on their own 650, particularly since I don't see too many of them on here. This site has been an amazing resource so hopefully this helps someone along through or at least you find some enjoyment in it.

Spencer

Here it is just after buying it:

[wolf550]

congrats on the bike and your build. those 70 tanks are the coolest version (i think) for the 650's.

[Spence_Ellis]

Agreed, they have so much versatility for customization, but are beautiful even if you leave the bike stock.

[Spence_Ellis]

Once I got it home, I began to remove the old electronics and parts that I knew wouldn't make it to the final bike. I removed the carburetors since I knew they needed to be cleaned, removed the airbox, turn signals, headlight, and gauges. I also stripped the red paint to give it a rougher look, which is what I was going for. I wanted something that had a consistent design ethos but wasn't too precious to be taken on extended trips or dinged at all.

After spending many cold nights in my unheated garage re-wiring the bike after removing the fuse box and all the handlebar instrumentation, I decided to bite the bullet and buy an M.unit. I was constantly blowing fuses trying to figure everything out and figured it would be a simpler and more streamlined process to start over. So with that in mind I kept going with what I could work on without electronics. It was a hard pill to swallow after crimping so many terminals, but that's life.

This all took place last summer, and during that time I replaced the rear suspension with parts from 4into1, installed a new halo headlight, clip ons, and cut the frame loop to make way for a new lower profile seat. Unfortunately, the bike had to take a back seat over the winter as we needed to finish the massive reno on our house that you can somewhat see in the pictures. Thankfully we are 90% done now, which makes bike work more possible!

[Spence_Ellis]

That pretty much brings us to current day. I purchased the m.unit and a lithium ion battery with upgraded reg/rec, and spent the winter figuring out how everything worked off the bike. (thanks to revival cycles). I wanted to keep everything under the seat so I made some cardboard mockups and made sure there would be enough space.

A few weeks ago my family went on a vacation and I finally had time to work on the bike in earnest, so I rolled it out into my dining room and got to work. I ultrasonic cleaned the carbs and found at least one problem right away. The fuel inlet is a little brass T that was facing down and the carbs needed to be separated to move it back upright. I'm not sure if it actually caused a problem but it was at least a giveaway that the job wasn't done perfectly by the PO. The carbs were a little dirty but not crazy bad, but I installed the new jets and new carbs kits from 4into1 anyway. With a new fuel line and a new petcock I finally had good fuel delivery. The petcock leaked at the threads out of the box so I used some Seal-All, which is a gas and oil resistant contact adhesive in the threads and it worked great.
There is a chin on the tank guide for running pods on this exact bike so I used that to guide my jetting. Fortunately I live in the country and am pretty close to WOT all the time, so I'm hoping I don't run into too many problems with the tuning since I love the look without the airbox, though I have read through a lot of the horror stories here and am willing to gamble with them for the time being.

With the carbs cleaned and reassembled, I replaced the spark plugs, boots, and condensers and then moved on to the m.unit wiring. I build a small electronics tray using step flashing and mounted the m.unit, reg/rec, starter solenoid, and battery. I'm running a 3 button left and 2 button right setup with mo.switches, and they had to be drilled, connected and routed before I could start it up. thankfully I was feeling patient that day because attaching those little tiny wires inside the switch housing is amazingly tedious, but it does give a great look and function. Once everything was connected I was super eager to get it going and amazingly it fired right up! The idle is way off and it was revving super high but at least it was running!

After that I mounted the seat with and it was off to get the frame loop welded on.

[Spence_Ellis]

Not sure why the thumbnails above are all weirdly oriented, but the actual photos are normal. After getting it running I couldn't resist the urge to go for a quick ride, so I put on the chain and took it for a spin around my backyard, only to find out that both the clutch cable and rear brake were almost completely useless, meaning stopping was more of a suggestion than a command. The clutch cable was shot and the rear brake was just horribly misaligned, but needless to say it was an exhilarating ride for a few seconds before killing the power. Once I got back inside I adjusted the rear brake lever and ordered a new clutch cable.

The front brake caliper had come in pieces from the PO and I had purchased a complete used one from ebay but the piston was seized. I took the advice of someone on this forum and used a grease gun to force it out which worked wonders, other than all the grease I had to deal with after. The piston had some small pitting, but the main culprit was rust on the back/bottom of the piston. I threw the whole caliper and piston disassembled into the ultrasonic cleaner and finished it with steel wool to get everything nice and clean again. I replaced the piston seal and it now moves much better. Hopefully I'll get a chance to get some brake fluid through it this week and see how it works.

I also decided to ditch the old digital tach and speedo combo I had purchased from Amazon, and went with the mini reproduction models from 4 into 1. The digital one never quite worked right, and everything I read said speed and tach were not as accurate anyway without the direct drive. In a stroke of good luck, both the tach and speedo fit on the existing mounting points for some of the old instrumentation, right between the clip ons. Eventually I want to get a small plate made that bolts into the original handlebar mounts to tidy up that area, but that's less of a priority atm. One thing I have noticed since I've replaced all the cabling is how much slack I have now that I run clip ons. The throttle cables were an absolute pain to route in a way that they didn't kink or bind with so much slack, enough so that I have to find another shorter B cable because there was just too much extra cable. I replaced the brake lines with SS and the tach and speedo cable and am facing a similar problem though they will fit. Whenever they get replaced, it'll be nice to shorten everything up a bit.

Once I get the brakes working 100% and the new instrumentation installed and mounted, It'll be time to start fiddling with the carb tuning. I checked the plugs after my first run through and it was running lean, so it will take some adjustment to get right I'm sure. I've never used a carb sync, but when I bought my original CB650 8 years ago a set came with it, so it'll be nice to finally get to use it after I get somewhere comfortable with the mixture screws.

[wolf550]

I really liked the brake caliper of my 79 650/550 frankenstein bike.
I liked that the caliper was held on by those massive bolts to the lower arm
and that the brake hose was one long tube going right to the master cylinder.
it seemed much stronger than the brake system on my 550's now.
I still have it for the next future project.

[Jimcg]

Good feeling being so close to driveable. Interesting to follow a fellow 650. 👍

/Jim

[SOHC4 Cafe Racer Fan]

Spence,

The 1979 CB650 was one of the first Honda bikes to use CDI in the form of 2 CDI boxes.  These early CDI boxes don't have the best reputation for longevity.  If yours decide to poop on you, there are new replacements available but you may consider adapting a Dyna electronic ignition.  Check out DaveBarbier's Patina Hyena build thread http://forums.sohc4.net/index.php/topic,140833.0.html

Dave adapted a Dyna kit for a 550 to 650 motor that is very reliable.  Dave also has considerable experience with rebuilding and tuning a 650 engine (albeit with a 674cc high compression piston kit).  Note: as tuned, his bike has a similar punch to a CB750 with an 836 kit in the lower weight of a 550/650 package.  Your 1979 CB750 frame has the same geometry as a 500/550 frame but has the benefit of a removable frame rail to ease motor ingress/egress.

[Spence_Ellis]

Thanks for that thread, that's a gorgeous motorcycle and a wildly detailed write up! I'll dive in later tonight, I'm sure there will be some valuable lessons there, even if I don't go as far as he did. That sense of patina or wabi sabi is the inspiration for this build, but I think mine will be much rougher lol. This will be a rider first and foremost and I can dig into design improvements as I go, but I would love the time and patience to make something that beautiful.

My CDI boxes have already leaked some of the black sticky stuff but they still seem to work, which I've read is common. I've found replacements but at $140US each, the dynatek would be a much better option, though it looks like the new coils I just installed are only 2.5ohms and would need to be upgraded. Maybe next year. I would love to do some longer road trips on this bike so reliability is certainly important, and I've heard that the dynatec really improves the power, which would be nice at highway speed on a 4 year old machine.

[SOHC4 Cafe Racer Fan]

Thanks for that thread, that's a gorgeous motorcycle and a wildly detailed write up! I'll dive in later tonight, I'm sure there will be some valuable lessons there, even if I don't go as far as he did. That sense of patina or wabi sabi is the inspiration for this build, but I think mine will be much rougher lol. This will be a rider first and foremost and I can dig into design improvements as I go, but I would love the time and patience to make something that beautiful.

My CDI boxes have already leaked some of the black sticky stuff but they still seem to work, which I've read is common. I've found replacements but at $140US each, the dynatek would be a much better option, though it looks like the new coils I just installed are only 2.5ohms and would need to be upgraded. Maybe next year. I would love to do some longer road trips on this bike so reliability is certainly important, and I've heard that the dynatec really improves the power, which would be nice at highway speed on a 4 year old machine.

The Dyna 3.0 ohm coils do improve the performance of the bike.  Keep in mind this solution, especially if your CDI boxes start to get wonky.

[Spence_Ellis]

So I was finally able to get the bike on the road for some short test rides. Initially it had a really hard time starting and was running super rich, so I turned the pilot screws in a little over a quarter turn and it runs great. They're probably 1.2 turns out now. Plugs look good now after a few rides at moderate speeds. No backfires, no sputters, takes about 5 minutes to warm up to run off choke but then runs like a dream with a nice stable idle. For the record it's got 120 mains, 42 slow jets, pods, and no muffler.

I'm not sure if this is connected to the pod conversion, but it's pretty tame until 5th gear, though acceleration is consistent through 1-4. Once it hits 5th it becomes an animal. WOT in 5th gear feels like a modern bike, which is awesome. Since I live in the country that's mostly where it will live, which is nice. I'll keep updating as I go, but I see this as a major win! Thanks for all the help!

[grcamna2]

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