I am the owner of a Honda motorcycle [CBX1000] who lives in Hiroshima City, Japan. I am posting about FCR carburetor and CBX1000 customization. I also post about things other than cars and motorcycles. We will post information that will make bikers around the world happy.
I want to synchronize the FCR carburetor myself after installing it.
The discussion is not limited to the CBX1000's six-cylinder engine but pertains to multi-cylinder engines in general. Many owners of multi-cylinder carbureted motorcycles might want to try synchronizing the carburetors themselves. For standard vacuum-type carburetors, frequent tuning is less common, and many people leave it to professionals. However, with racing carburetors like the FCR, tuning it yourself is part of the fun. Being able to synchronize the carbs yourself expands your tuning possibilities. I will write columns focusing on synchronizing the FCR on my CBX1000. Past posts have also covered synchronization, but I won’t focus on the specific methods here. Instead, I’ll discuss the enjoyment and importance of being able to synchronize on your own. For specific methods on synchronizing the FCR, please search the site using keywords like “synchronization.” Let’s get started!
Is there a problem if the synchronization is not perfect?
The accuracy of carburetor synchronization is considered complete when you are satisfied with it yourself. If time constraints or persistent issues prevent perfect synchronization, it's okay to be less precise. After all, you'll likely need to redo the synchronization work at some point. When the engine is hot, the cylinder with higher RPMs will pull the RPMs of the cylinder with lower RPMs down. Conversely, when the engine is cold, the cylinder with lower RPMs will be pulled by the one with higher RPMs. Low synchronization accuracy can lead to poor RPM drop during revving. If synchronization is significantly off, it can cause the RPMs to not drop properly, which is dangerous. As long as the synchronization does not affect performance, it's generally not a problem. Synchronization is a matter of personal satisfaction. However, if you are working on FCRs as a hobby, you should strive for accurate synchronization without compromise.
Synchronizing a carburetor with a dual throttle cable setup is quite a hassle.
For types like the CBX1000 and some Ducatis, where the throttle cables are split into two branches, resulting in a total of four cables (pull and return), synchronizing carburetors with two reference carburetors is quite labor-intensive. It's not so much difficult as it is time-consuming. There are two main reasons for this:
①The tension of the throttle cables must be perfectly matched. ②The height of the idle stop screws must be precisely adjusted.
Even if synchronization is perfect at idle, a slight movement of the throttle by just a few millimeters can cause the synchronization to shift. This happens for two reasons:
①Each cable has slightly different clearances. ②If the height of the idle stop screws is not correct, the throttle opening at the
beginning of the throttle movement will vary. These are very small discrepancies. Achieving perfect synchronization requires careful attention. It is necessary to prioritize synchronization that provides good throttle response during revving according to your personal preference. I consider a throttle response that is good during revving as an indicator of proper synchronization.
Calibration of multi-vacuum gauges is essential.
Most people typically use a 4-gauge multi-vacuum gauge. I have modified two 4-gauge multi-gauges into a 6-gauge setup for faster operation. The reason is to speed up the process. Excessive engine temperature is not pleasant, so I've opted for a 6-gauge system to save time.
Initially, I used to connect and disconnect the hoses on a 4-gauge setup to synchronize the carbs. I noticed something seemed off a few times. When I calibrated the gauges, I found significant imbalances between them, rendering synchronization meaningless. I was shocked when I first realized this, but I'm glad I noticed it.
Always ensure that your vacuum gauges are calibrated before starting synchronization work.
When synchronization is correct, the idle feel is noticeably different.
At moments when synchronization is well-balanced, you may feel the engine's sound pulsing during idle. There should be a noticeable change when you achieve proper synchronization. I believe the goal of synchronization is to improve engine RPM drop. Synchronizing is not the ultimate priority, but riding a motorcycle with excellent synchronization is certainly enjoyable.
FCR Beginners – Let’s Start Synchronizing!
The blog I write focuses on personal DIY projects. I enjoy motorcycling by having work done by motorcycle shops while also indulging in DIY projects myself. Synchronizing carburetors is a choice of whether to do it or not. It’s almost impossible to fail if you try. What amateurs can't achieve is perfect synchronization; you can only reach a level of synchronization that’s perfect in your own way. Some mechanics might say that perfect synchronization involves various factors like engine condition and compression plugs. Synchronization work doesn’t lead to irreparable mistakes if you try. As long as you don’t intentionally make a mistake, it won’t render your bike unusable. I encourage you to give it a try.
I want to synchronize the FCR carburetor myself after installing it.【summary】
I believe that performing motorcycle maintenance yourself is something cool. It's important to engage with your motorcycle within the range of what you can handle. By doing maintenance and cleaning, you gradually learn more about your bike. Carburetor synchronization is actually one of the simpler tasks. The first step is to gather a basic set of tools, which you might already have on hand. If you haven't tried it before, I encourage you to give it a go with an open mind. See you again!
CBX1000 Photo Gallery
I will be featuring past posts with photos focusing on the carburetor synchronization work.
