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.
FCR Tuning – Re-synchronization after adjusting the throttle cable – 2023-08-01
"I synchronize the FCR carburetors on my CBX1000 more than 10 times a year. Whether 10 times is a lot or not, I'm not sure. It's not that I feel the synchronization has drifted while riding and then readjust it. Instead, it's because minor misalignments occur when I tune the FCR and have to remove and reattach parts.
The main reason for this misalignment is the dual throttle cables. My CBX1000's FCR is an older model, with two sets of three linked FCR carburetors: a set for cylinders 1-2-3 and another for cylinders 4-5-6. The throttle cable splits into two along the way, and there are two idle stop screws. This setup can lead to slight misalignments when parts are removed or reattached.
Every time I make tuning adjustments, I re-synchronize the carburetors. While minor misalignments are within the acceptable range, I always perform a re-synchronization if I've done something that could cause a significant shift, such as adjusting the throttle cable tension or touching the idle stop screws.
A lot of users are interested in carburetor synchronization and often ask me how I do it or want to see the process. In this blog post, I'll be writing about FCR synchronization, focusing on my CBX1000 with the dual throttle cables. This might not apply to many other motorcycles, but if you're in a similar situation, I hope you'll find this helpful.
So, let's get started!
Is it better to perform synchronization frequently?
I frequently perform FCR synchronization. There are benefits to doing synchronization regularly. Since the misalignments are usually minor, the work can be completed in a short amount of time. If the synchronization has drifted significantly, it can take a bit longer to complete the task.
The actual synchronization process of the FCR often takes less time than the preparation, such as removing the fuel tank. A slight misalignment in carburetor synchronization doesn’t necessarily mean your motorcycle will run poorly. However, if the engine idles too high when the temperature rises or if the RPM doesn’t drop easily when you fully close the throttle, then synchronization is necessary.
An engine that doesn’t reduce RPMs quickly can be dangerous while riding. Let me explain the symptoms when the carburetor synchronization is off. When the oil temperature is low, the engine refers to the carburetor with lower vacuum. When the oil temperature is high, it refers to the carburetor with higher vacuum. The right time to perform synchronization is when you notice that the engine’s RPMs are slow to drop.
Even a slight adjustment to the air screw can cause the synchronization to shift.
Synchronization can shift even when adjusting the air screw or pilot screw. During this task, I noticed something important. When I made a significant adjustment to the air screw, the resistance when twisting the throttle changed considerably. I adjusted the air screws uniformly across all cylinders. The change in resistance indicates that adjusting the air screw greatly affects the vacuum pressure.
In a multi-cylinder engine, each cylinder has different conditions. Even if you adjust the screws in the same way, slight differences will appear. Ideally, you should perform synchronization even if you only adjust one part of the carburetor. However, synchronization doesn’t usually have a significant impact on normal riding. Considering the cost of the work, minor misalignments should be ignored.
In my case, I tune the FCR for a hobby. Since I aim to maintain optimal performance as much as possible, I frequently perform synchronization.
Should you use a fan?
HONDA CBX1000 – FCR tuning electric fan
Using a fan is recommended if possible. Even idling the engine for an extended period can cause the oil temperature to exceed 100°C, leading to oil degradation. If the engine needs to run for more than 10 minutes, I use a fan or other cooling measures to manage the temperature before proceeding with the work.
FCR Beginners’ Guide – How much synchronization work should be done?
Synchronization work is a goal-oriented task. The level of synchronization should be as perfect as you aim for. At a minimum, if you feel that the engine’s RPMs are not dropping properly while riding, synchronization is essential. It's quite challenging for beginners to achieve perfect synchronization. With practice, you'll be able to complete the synchronization process more quickly. If the misalignment is minor and within an acceptable level, it’s okay to consider the task finished.
FCR Tuning – Re-synchronization after adjusting the throttle cable – 2023-08-01【summary】
Regarding the cables, there are a few things to check. Ensure that the throttle openings are synchronized at the start and that the throttle valve heights are aligned across all cylinders when the throttle is fully opened. If you have only two throttle cables for opening and closing, you might not need to be as meticulous. However, with a dual cable setup, touching the throttle cables can disturb the overall balance.
If you’re working on FCRs as a hobby, you can spend a lot of time on it. Even if things don’t go well, it becomes part of your experience. Beginners should accumulate tuning data during the first year. By the second year, you will have last year's data to refer to. If the performance drops, you can resolve issues by tuning it similarly to how it was when it ran well last year. Without tuning data, you’ll need to start from scratch.
This time, we discussed carburetor synchronization. See you again!
