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Jul. 4th, 2023

Upgrades on 'Ruth' for the 2023 riding season.

Some regularly scheduled maintenance, and some just for fun...


Ruth was becoming a little unreliable if I'm being honest — which was, to be fair, somewhat expected given she's approaching the 50-year mark. But, as I sat there trying to re-start her after a one-way trip from my apartment to Harvard campus (a distance of about 3 miles), I decided that was a little much. Yes, these old CB's are from a while ago but they actually run pretty smoothly over long-distances if treated well, maintained properly. So in this case I blamed myself for not cleaning the carbs or replacing the spark plugs earlier.

In the last post about Ruth, I mentioned a list of upgrades from about a year ago I wanted to do 'later' on the bike. This post will focus mostly on those. My goal this summer is to make Ruth as reliable and convenient as possible, and to reduce some of the signs of her age such as rust, and chipping paint. Here's a list of what I want to do.


  • Replace the Carburetors with newer modern ones I can get the parts for during cleaning, I attempted to get a cleaning kit for the original, stock carbs but some of the parts were over-sized or simply didn't fit properly. I was worried they would do more harm than good.

  • Tune the engine and the idles properly, last time it was done kinda arbitrarily and it was one of the reasons the bike idled so high in the rev range. I want to prevent the bike from cutting out at lights as well, sometimes I have to hold the throttle open.

  • Fix the electric starter, possibly by replacing the motor, at the very least by hooking up the current motor to a starter solenoid. 

  • Fix the alternator, maybe not necessarily to re-charge the Milwaukee M18 battery I put in there, but at least to power the bike during operation and use the battery just to start the vehicle. 

  • Fix the exhaust as well as the rear mufflers, there's a lot of paint chipping and other various degradation seen in that system.

  • I want to replace the headlight, mirrors, remove the handlebar guards I added, and make some other small, aesthetic changes to give her a cleaner, more modern-retro look.

  • Then the standard replacement of spark plugs, checking the tyres, batteries, and other parts of the electrical system, loose bolts, and etc.

  • Add a tool kit somewhere, maybe some saddlebags, possibly add mud-guards or fenders to the rear wheel.

I'll break this up into a few sections since there's a good amount of work to be done.


Starting with the engine, fuel system, and tuning — which is, by far what the bike needed most. After searching around for a while on the internet, I landed on the VM30 Mikuni Carb kit from SpeedMoto mostly because it felt the most complete, coming with air filters (if you want), and a split throttle cable out of the box. I didn't choose any of the stock air filter options because I've had trouble getting larger air filters on by bike before, so I went with "wider" but "shorter" KN-type filter pods, also from SpeedMoto. I also got spark plugs from Common Motor, the standard NGK BR8ES plugs that come on the bike. It took about a week for all these parts to arrive. I referred to the following list of videos when figuring out how to install everything, but I'll also describe the process below.


Before I did anything, I started by closing the petcock valve and disconnecting the fuel lines that lead to each carb. I drained the fuel into a storage container for later disposal. It's pretty critical that these products get disposed of properly for environmental reasons, but also for the safety of other people. Here's a guide for how to dispose of this stuff in MA, but you should be able to google the regulations for your own town.

aking the old carb and air filters off was easy enough, just un-did the tube clamps holding everything together and wiggled them back-and-forth until the rubber loosened and they came off. The throttle cable was slightly harder to remove and had to be disconnected at both ends, and I had to disassemble the switch-box on the handlebars to get the cable out. Once that was done, I took a screwdriver and started to remove the manifold boots that connect the carbs to the engine block. It's critical that you use the right size screwdriver head for this, one that fits snugly, especially for these older rusty screws. If you strip these screws they'll be very difficult to take out, and metal shards could fall into the engine intake. Go slow, and apply axial pressure to the screwdriver. 


The Mikuni V30 carbs came with their own new, dedicated boots. I tried fitting the carbs onto the old boots just for fun but they didn't fit so the new boots are required for installation. This is a good idea anyways because then you don't need to worry about fixing small tears in the rubber on the older boots. The alignment of these boots doesn't matter too much.

The area around the engine intake (under the boot) was showing some signs of rust. I did not de-rust or touch this area because I hoped that covering the area with a new boot and adding machine oil would stop further degradation. I may remove the boots and clean this area later, but I may also do an engine re-build in about a year and I'm saving this work for that time.


The carbs came pretty much fully assembled with the exception of the throttle cable and the fuel lines. The three pink-colored tubes that are connected to the carb out of the box are drainage tubes that you don't need to connect anything to. The tall brass inlet on the left side of the carb is where the fuel line connects. The thumb-screw with the spring, also on the left side of the carb is the idle adjustment screw. On the right side of the carb, the small brass flat-head screw right by the air intake is the air-fuel ratio screw. We will be adjusting both of these screws during the tuning process. 

I started by placing the air filters on the back of the carb and using the tube clamps to clamp them onto the carbs. I assembled them as a unit off the bike so there would be less assembly to do when everything was connected to the engine. The CB360s don't have a huge amount of space to get your hand in and work on the bike in the region where the carbs and air filters sit. 

It's also important to note that the stock CB carbs have their chokes, idle screws, and throttles all connected. They come as a unit of two carbs and both carbs can be adjusted together. We are replacing this unit of two carbs with two individual carbs. Each carb has its own throttle connection, air-fuel ratio screw, idle screw, and choke. All of which have to be tuned individually. This is both a dis-advantage and an advantage. It makes tuning harder, but it also allows you to tune each cylinder more precisely. 


The next step was to deal with the throttle cables. And frankly, I didn't care much for this design. I though there were many better ways of designing this throttle cable assembly that didn't involve disassembling the carb and passing the cable through a spring and various other assemblies. It was difficult and uncomfortable to say the least, and it had to be all done on the bike as well depending on how the throttle cable needs to be fixed to the rest of the bike. Ew. Do better. Anyways here's what I did. 

First, I attached the new throttle cable to the handlebar throttle so I could figure out how to route the cable through the bike. I turned the steering to full lock both ways so I could make sure it had enough space as to not pull on the throttle while turning. The steel throttle cable splits into two, forming a "Y." Each side going to one of the two carbs. Once the throttle is fixes this is where the problems really start. The videos above show how to assemble the cable but I struggled to compress the spring enough during assembly to get the cable in. Finally, I decided to zip-tie the ends of the spring together so I could pass the cable through and fixture it to the throttle slide without having to hold the spring closed. That made things a lot easier. Once the cable was in the slot, I snipped the zip-ties and slowly released the spring into place. Then I went onto synchronization.

When you have more than one carb in a system, synchronization is an important step. Syncing your carbs is basically to make sure they open and close at the same time, and one throttle isn't "more" open than the other. This is especially important when you have two independent carbs where the throttles are not connected. 

To sync these carbs, I let them rest on the engine block with the throttle cables attached and roughly in their final position. I "revved" the throttle open and closed a few times and let the throttle slides settle into a position. Then I used the idle screws to adjust the position of both throttle slides to be at the same level.

The idea here isn't so much to get the final "idle" position right, but to get the slides to the same position on the left and right carbs. So when we get to adjustment of the idle speed of the system, we can adjust both screws the same number of turns and the slides will move up and down together so each cylinder is getting the same "throttle" signal. Having the valve be more open on side or the other makes the engine run less efficiently and causes asymmetric wear on the engine as one cylinder takes more load than the other. It also limits the maximum output power of the engine. After syncing, we are ready to mount the carbs.


The mounting itself was fairly straight forward. I started by slipping the pipe clamps over the rubber boots, and then wiggled the carbs onto the boots one at a time, tightening down the clamps was straight-forward. It's just important to make sure the clamps are positioned correctly so as to not "push" the carb off the boot rather than clamping it to the boot with radial pressure.

I also zip-tied the throttle cable in strategic places so it wouldn't come apart, or flop around. This cable needs to be secured well and the best way to do that depends on the layout of each bike. I used the main wiring harness that runs the length of my bike to secure it. If not secured properly, the cable could "pull" on the throttles asymmetrically and cause the carbs to go out of sync, or open the throttle as you steer the bike which would not be ideal. 


The last thing to be done before tuning was to replace the spark plugs. I used the standard NGK BR8ES plugs, nothing fancy. But new ones were really needed. I took the old ones out and there was significant cowling and some degradation on one of the ground electrode of the plug. Here's a good labeled diagram of a spark plug for reference.

A good thing to note here that tripped me up for a few minutes, is that these spark plugs have caps on their terminals to protect them called "terminal plugs." You need to unscrew these before attaching the spark plug cable to the actual spark plug. Otherwise the cable won't fit or conduct. Initially, I thought I had bought the wrong plugs but I was being silly.

The next steps were to tune the bike. This was a little tricky because I hadn't done it before, and I had to tune two individual carbs to work together nicely rather than a single set of tuning knobs for both carbs. But first, I'd recommend getting something like the Autool DM301 automotive tester or some other inductive-pickup RPM sensor. To tune the engine properly, we need to be able to measure the RPM of the vehicle. If you have a newer bike, you might have a rev counter which could work as a good measure of RPM given you trust the instruments. My rev counter is broken, and even if it wasn't I think I would still sanity check it with something given the age of the vehicle and the possibility the counter could've gone a little out-of-wack. But I chose to go with this inductive RPM sensor which basically counts the rate at which the spark plug fires and uses that to back-out RPM (it's 1:1 basically).

Here was the strategy I used to tune the carbs, every carb is a little different and requires some finesse. I feel It's easier to know what to listen/feel/look for rather than follow a specific tuning procedure and retune as needed after you ride a few times. That being, I'm no expert in this area. I want to learn more about this stuff in general.


  • I started by just increasing the idle on both the carbs until it would just run when I kick-started the bike and I didn't have to hold the throttle open. I let it run for a few minutes to let the engine warm up.

  • Next, I put my hands behind the exhaust pipes, and made sure exhaust was coming out from both at the rate I expected. You should feel a "puff" from each exhaust when a cylinder fires. One exhaust was running much hotter than the other. So I reduced the richness of the fuel in that one by adding more air to the mix, and then increased the richness of the fuel in the colder exhaust. I did this basically until I could get the temperatures as even as possible. It's not perfect, so I'll probably revisit this later.

  • Then I took out the DM301 multimeter and lowered the idle screws together until the engine was firing at around 1300 RPM, it wouldn't run lower than that so I re-tightened the idle screws just until they contacted the throttle slides again. The engine remained at 1300 RPM. Note that this is still a little high, we want the idle for these bikes to be around 700-1000 RPM. 

  • Then I went for a long ride, about an hour. This was to make sure that everything felt OK but also to allow everything to settle into place. Running your engine in and varying the throttle is always a good idea to allow the parts to settle into natural lower-energy states and remove any weird "pulling" or "pushing" stressed caused during assembly. When I got back, the idle had lowered itself to around 1035 RPM. So I decided not to touch it.

It remains to be seen if this setup is good enough for carb tuning, I might take the bike over to my friends at Madhouse Motors in Boston to get some tips on tuning the carb. But the bike felt really good on the road. No signs of cutting out and the acceleration, and smoothness of the ride really improved with the new carbs. These carbs are great! Would recommend for your next build if it wasn't for the stupid throttle assembly.

The video on the left (above) is the bike operating at around 3000RPM idle, that's when I first kick-started it and adjusted nothing. You can hear the idle is higher than it should be and a slight imbalance in how the cylinders are firing. The video on the left is the bike after all tuning and the 1-hour ride. You can hear the idle has settled and the cylinders are firing in a slightly more even rhythm. That's what a bike should sound like, and the temperature of both exhausts should be similar. This is a good reason to keep your exhausts separate so that tuning imbalances out is easier.

Update—after taking Ruth out for a ride I noticed the throttle was cutting out when I stopped at a light and one of the exhausts was popping. So I did the following:

  • I re-tuned the air-fuel ratio, I moved both screws to the middle and then turned them to either side while listening to the noise the engine makes. At the extremes, the engine RPM starts to "sag" but at a good air-fuel ratio, the engine RPM sounds "healthy," it's usually the highest RPM as you turn the air-fuel screw.

  • I also re-tuned the idle to be around 1300 RPM, it's a little high, but it helped the throttle cut-out issue. Now, after the engine warms up, the throttle no longer cuts out.


Now onto fixing a few other parts of the bike — I've been meaning to do some of this for a while. I had to order a few other parts. I put what I ordered in the list below in case any of you want to replicate any part of this build.

The install of the headlights and the turn signal relay was fairly straight-forward. I cut out the bi-metallic strip flasher and replaced it pretty much exactly with the LED flasher. The idea here is it can flash the turn signals without the high currents required to activate the bi-metallic strip. I like this solution better than the regular power resistor people use because it draws less current. 

For the headlights, the only thing I had to figure out was how to deal with the turn signals that were already mounted to the plastic case of the original light. Annoyingly, I had to cut the wires and re-wire the signals. But this time I used the turn signals as intended in terms of mounting. They're designed to "replace" the bolts that hold the light onto the mounting brackets, so I screwed them in and then re-wired everything inside the "dish." 


I added that classic "cafe racer X" tape to the headlight to maintain the previous style, and then moved onto the grips and the mirrors.

The mirrors was a bit of a fun situation. Either, this mirror only comes as a left-hand side mirror, or I ordered two "lefty" mirrors. Either way, something to be careful of if you choose to go with this mirror. I solved this by unscrewing the actual mirror part witch a wrench which was held into the aluminum mount using Loctite. And then screwing it into the opposite side after removing the decorative screw (also held in with Loctite). I did add blue Loctite when screwing the mirror back on. Installing them on the handlebars was straight forward.

The grip tape was pretty easy too, I just followed the instructions. I started with the "fat" side of the tape as one end tapers off, and I started by wrapping that around the outside edges of the handlebars working my way in towards the controls. They're a little "thinner" than my previous grips but I like their feel. The throttle side went on easily without any modification too which was really nice. Didn't affect the operation at all. 

Finally, the exhaust wrap you see. I followed the instructions for this as well. But one recommendation I do have is to get thicker gloves. The wrap frays when you cut it (that's pretty unavoidable), and the tiny fibers in the wrap make for some pretty nasty, uncomfortable splinters. Other recommendations I have would be remove the exhausts off the bike if you can, it makes wrapping easier. And if you have a second person who can give you a hand with passing the roll around the exhaust while you keep the wrap tight, it helps a lot. Shoutout to Francis Wang for helping me out here!


And voila! I actually used a different style of photography for the final photoshoot for this bike. To get these photos I masked the background and actually reduced the white-balance temperature on the background only while leaving the bike at the correct white balance to make it "pop" a little bit. I also masked the tank and reduced highlights just in that area to get the tank letters to look a little cleaner. I'm super happy with how the photos turned out I think they capture the new 'look' of the bike really well. 

But overall this was fun and successful! She's all ready for the rest of the riding reason. She's been running really well since the new carburetor and the other other upgrades have cleaner up her look from what it was previously. I think the restore is almost complete with the exception of a few small details. But those are to come in the future. Love this bike so much.

#motorcycles #restoration #caferacer

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