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 – Lean slow jet – Changed from 48 to 40 – 2022-07-03
This article focuses on replacing the slow jet (SJ). Due to rain in the forecast, I decided to skip the test run and just replace the SJ.
In most areas of Japan, there is heavy rain from June to August.
The change was from SJ-48 to SJ-40.
Although SJ-42 might be a better choice since it is the default value when BITO is shipped, I wanted to verify the difference myself. Therefore, I opted for SJ-40, which is lower than 42. Since I enjoy tuning the bike myself, I wanted to try something a little different from BITO's initial settings.
work photos
I often check the condition of the carburetor by removing it and inspecting it from the side. It's been a while since I last did this. When replacing the slow jet (SJ), if you remove the carburetor and turn it over, be aware that debris can sometimes get stuck in the float valve, causing overflow. I make sure to tap it lightly before reinstalling it to dislodge any debris. Additionally, I always check the play and return strength of the throttle wire. Replacing the SJ took me about 30 minutes, as I took my time with the process.
It's a good idea to prepare a spare chamber gasket in advance. While it's possible to reuse the gasket, it can be very troublesome if it becomes unusable due to repeated attachment and detachment.
For my CBX1000, I carry a quick-release O-ring for the fuel line and a clip for the jet needle. These items are not expensive and can usually be found at a home center. However, the chamber gasket used when replacing the slow jet (SJ) is often not readily available due to its special shape, so it's best to keep a few spares on hand.
Since tuning is often done outside, being unable to run the bike due to a lack of essential parts can create a difficult situation, especially for beginners. It's important to be well-prepared.
For FCR beginners ② – Rules for slow jet change
Here are some guidelines for replacing slow jets:
1. Minimize Replacement: Once you have chosen a slow jet, it’s generally best not to replace it frequently. Adjustments should be handled with a screwdriver whenever possible.
2. Idling Check: If you can maintain idling with the pilot screw (PS) fully closed, the slow jet is likely too large. Conversely, if you can't achieve idle even after adjusting the PS to 3.30 minutes, the slow jet might be too small.
3. Alternative Adjustments: You can modify the effect of the slow jet by changing the straight diameter of the jet needle or the clip stages. However, this approach can be tricky, especially for beginners who may not have multiple jet needles.
4. FCR Tuning Manual: According to the FCR tuning manual, the slow jet should be replaced when the screw adjustment exceeds its range.
5. Systematic Tuning: The basic approach to tuning is to fix certain components and change one part at a time. This method is a practical shortcut when you're unsure of the outcome.
6. Needle and Jet Interaction: The number of clip stages and the straight diameter of the jet needle can influence the choice of a slow jet, but significant changes in jet needle size are usually required to affect the slow jet selection.
7. Incremental Adjustments: If you notice issues after replacing the jet needle in the intermediate range, try changing the slow jet one step at a time based on the jet needle settings. This incremental approach often leads to better results.
By following these rules, you can achieve a more effective and manageable tuning process.
FCR tuning – Lean slow jet – Changed from 48 to 40 – 2022-07-03【summary】
Lately, as I’ve become more accustomed to installing and removing carburetors, I’ve found myself becoming less attentive and occasionally forgetting to tighten screws. I’m not the type to maintain concentration for long periods, so I always double-check everything after I’m done. Even so, I sometimes still forget to tighten the screws. Please be careful not to overlook this.
This time, while working at my parents’ house, my neighbor’s wife asked,
“Did your motorcycle break down again?”
Hearing this twice made me realize something was amiss. It’s not actually broken, but I can’t confidently say I’ve set the carburetor correctly. I had to apologize for the inconvenience caused.
I usually replace jets at my parents’ house, but for synchronization work, I prefer to go deep into the mountains. Please avoid doing synchronization in residential areas, apartments, or parks. Japan has many densely populated areas, so it’s important to choose an appropriate location for starting the engine.
Wishing you a great experience with FCR tuning. See you next time!
