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 – JN Jet Needle Straight Diameter and Clip Position – 2023-05-03
Previous Tuning After changing the main jet in the last tuning session, I’ve felt a noticeable power increase in my CBX1000. I’ve been curious about trying out changes to the slow jet and jet needle as well. There’s an event in a few days where CBX1000s will be gathering, so I want to make sure everything that’s been on my mind is properly checked beforehand. When tuning the FCR, I generally avoid touching the SJ (slow jet) unless it’s beyond the adjustment range of the AS (air screw). For this reason, I decided to change the JN (jet needle).
I’ve changed the clip position from #1 to #2. Changing the straight diameter or the taper angle can shift the optimal position. Since I’ve made the straight diameter leaner, I’ve adjusted the AS towards the rich side. I tightened the AS from lean to rich, checking in 5-minute increments by repeatedly performing stop-and-go tests until I found the position with a strong sense of power during acceleration.
Impressions after the test ride
I’ll share my impressions after the test ride following the tuning. In conclusion, I feel like I need to make one more fine adjustment. The current tuning is already very good, but I want to see if there’s an even better combination of jet needle straight diameter and clip position. I’m considering whether to lean out the straight diameter by one step from R to S, change the clip position from #1 to #2, or perhaps do both.
It might also be a good idea to start over by changing the SJ (slow jet) from 48 to 45. However, avoiding too many changes to the SJ is my general approach. I have a strong preference for the 48 SJ, and I’m reluctant to lower it to 45 or 42. Tuning with a 48 SJ and straight diameters of [Q], [R], or [S] seems to work well. Changing the JN (jet needle) instead of the SJ is quicker and allows for more comparison tests.
FCR Beginner Guide – Being Mindful of Work Time
I consider tuning the FCR carburetor to be a process of comparison. For rough adjustments, it might be acceptable to make changes all at once without comparison. However, for fine-tuning, it’s essential to determine whether the current setup is better or worse compared to the previous tuning. If multiple jets are changed simultaneously, it becomes impossible to make a meaningful comparison. Therefore, it’s crucial to change one aspect at a time.
For example, if a jet change leads to a worse performance, it indicates that the previous tuning was in a good state. Until you compare, you won’t know whether the current tuning is good or not. With experience, one might be able to judge whether the condition is good or bad and skip some comparisons, but beginners should evaluate the tuning results by making several comparisons.
Regarding being mindful of work time, FCR tuning should involve deciding beforehand which aspects to change. You should always visualize what will be leaned out or richened before starting work. If there are multiple options, choosing the ones that require less time will increase the number of comparisons you can make. This doesn’t mean that you should only focus on easily changeable aspects, but rather that being aware of work time can expand your options for jet changes and increase your comparison materials. In the past, I used to tune without considering the time involved. Generally, having more comparisons tends to provide better data for tuning decisions.
In the above, I changed the clip position and straight diameter simultaneously.
90FTR #1 → 90FTR #2
Changing the clip position dramatically alters the feel. Verifying through actual riding is more important than comparing the air-fuel ratio. Based on past experience, I changed two jet needle positions simultaneously. Since these are relatively significant changes, changing the clip position is one of the reasons for this.
FCR Tuning – JN Jet Needle Straight Diameter and Clip Position – 2023-05-03【summary】
Tuning is something I do not because I have to, but because it’s one of the joys of riding. The changes I’m making this time aren’t necessary to keep the bike running; I’m doing them to expand my knowledge and understand the differences. The moment I seriously consider revisiting my tuning is when I get overtaken on a straight by a bike of the same era. I hope you all stay safe and avoid any accidents or troubles, and enjoy your motorcycle life to the fullest. See you again!
CBX1000 – Photo Gallery
These are photos of the jet needle changes.
The first photo shows the jet needle being removed using a protective cover for the connectors.
The photo without disassembly is from the test ride.
