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 – To What Extent Should Carburetor Synchronization Be Done?
How Far Should Carburetor Synchronization Be Done?
Many people are likely wondering to what extent they should synchronize their carburetors. Vacuum gauges have graduations. Is it acceptable for the reading to be off by one graduation? Does even the width of the black line on the gauge count as an error? If you keep thinking about it, there’s no end.
The other day, I got the answer. Here’s what I was told:
"Vacuum-operated carburetors should be perfect. For FCRs, visual alignment is good enough."
This came straight from Mr.Bito of BITO R&D, so there's no doubt! This is a valuable opinion from one of Japan’s legends. This might also be a response considering the requirements, the use, or time constraints. For vacuum-operated carburetors, he said they should be perfect. Perfect synchronization means doing it as perfectly as one can manage.
For FCRs, my interpretation is that even if the synchronization is slightly off, it’s not something to worry about as long as it doesn't greatly affect the ride. That said, there’s no harm in achieving perfect synchronization as far as possible with FCRs as well. I personally believe that synchronization work on FCRs should be done as perfectly as possible.
Now, let me share my own thoughts on synchronization precision. "If there’s no problem with how the engine returns to idle, that’s good enough." Even if there’s a slight difference in the gauge reading, it doesn’t affect the ride. However, issues with how the engine returns to idle do affect performance.
In the next section, I will focus on what is meant by "visual alignment." Since this is a blog about FCRs, I won’t be discussing vacuum-operated carburetors much.
Important Precautions When Synchronizing Using a Multi-Vacuum Gauge
There is a mandatory procedure when using a multi-vacuum gauge: calibrating the needle balance.
When I bought a brand-new multi-vacuum gauge and tested it, the needle balance was off by one graduation. Performing synchronization without calibrating the needle balance is entirely meaningless. You can't verify if you're correctly measuring vacuum pressure without calibration. At the very least, the goal is to balance the vacuum pressure across all cylinders. As long as the needle balance is correct, you can achieve the purpose of adjusting the synchronization.
I use a syringe-type pump and a vinyl tube to adjust the vacuum balance. As for the specific adjustment method, you can calibrate by pushing or pulling on the needle's pivot. The picture shows a six-gauge setup, but I’m using a four-gauge multi-vacuum gauge with two additional gauges added.
For FCR Beginners – Synchronization is Not Important for a FCR.
When writing for beginners, the straightforward advice is to say, "You don't need to worry about synchronization." A common assumption for beginners is that they don’t have all the necessary tools. In some cases, motorcycles require modifications to extract vacuum pressure for the first synchronization attempt. The first challenge beginners face is preparation.
FCR Tuning – To What Extent Should Carburetor Synchronization Be Done?【summary】
Until now, I have been performing FCR synchronization with what I consider to be a perfect setup. Mr. Bito mentioned that visual alignment is sufficient. In my case, I tune FCRs as a hobby, so I have all the time in the world. On the other hand, when I’m pressed for time or feeling physically or mentally drained, I can approach the adjustments more casually, thinking it’s okay to skip some steps. I have previously written articles about FCR synchronization. I also include information about the necessary tools, the addition of vacuum extraction nipples, needle calibration, and more. For those who are about to take on synchronization adjustments, please make good use of the search function on the site. See you again!