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 – Changed from MJ(Main jet) 125 to 120 – 2022-06-18
Regarding CBX1000 FCR tuning, I mainly focused on adjusting the MJ main jet. The current setup isn’t in bad shape, and during expressway driving, the air-fuel ratio was around 12.5 at both full and partial throttle openings. However, it’s challenging to accurately measure the air-fuel ratio during partial throttle and acceleration due to the difficulty in maintaining a consistent throttle position.
This time, I aimed to make the MJ richer and observe the changes in throttle response between 1/2 and 3/4 throttle openings. Even if the MJ remains on the richer side, it seems acceptable. Adjusting the acceleration feel at 1/2 to 3/4 throttle openings should be possible.
While the current settings are generally fine, I’m looking for ways to enhance acceleration. The throttle response feels a bit off when not precise, so I’d like to improve that as well. I anticipate that a richer tuning will yield better results. If time permits, it would be beneficial to also adjust the number of clip stages on the JN for further refinement.
work photos
I haven’t removed the tank, but after removing the FCR, I replaced the MJ main jet by removing the drain bolt at the bottom. Please note that the photo of the main jet is out of focus.
Current tunings AS-1.30 minutes return PS-1.15 minutes return SJ-55 JN-90FTR#2 MJ-125 → AS-1.30 minutes return PS-1.15 minutes return SJ-55 JN-90FTR#2 MJ-120 @I only rode it a little, but the feeling is better with a larger MJ → AS-1.35 minutes return PS-1.15 minutes return SJ-55 JN-90FTR#2 MJ-132 @I get the impression that it has become richer overall, I feel like the discomfort I had when opening the throttle suddenly has been alleviated, but around 1/4 of the throttle. It feels heavy, so it may be necessary to consider lowering SJ or changing the straight diameter of JN. I might be able to finish it by just adjusting AS, but I would like to try adding a little more information about MJ. Around 138 would be appropriate, or the current 132 would be appropriate. The feel itself is also good.
FCR-For Beginners – MJ Change
This advice is aimed at beginners, and professionals using Dynojet or those with their own advanced theories might not find it applicable.
When replacing the MJ main jet, start by trying values like 10, 7, or 8 to gauge the effect. It's useful to focus on throttle openings around 1/2 to 3/4, as opportunities to test full throttle are rare. If the tuning is good around 1/2 to 3/4 throttle, the MJ setting for full throttle should generally be close to optimal.
I’ve driven at full throttle for about a second with MJ102, and the piston didn’t melt. This discussion pertains to tuning limits at 9200 RPM with the CBX1000. Currently, my limit is set at 10200 RPM, and I haven’t tried settings below 115.
Once you find a good tuning, consider rechecking the MJ setting at full throttle. Tuning at full throttle can be challenging for less experienced riders without an air-fuel ratio meter or a dyno. Without an air-fuel ratio meter, obtaining precise numerical data is difficult. As an amateur with no circuit or advanced machine experience, I rely on the tunings that seem correct.
Arriving at the right settings takes time and experience. You’ll need to intentionally adjust towards richer and leaner settings to find what works best. Even with an air-fuel ratio meter, the complexity of tuning remains significant, but the meter is a valuable tool for beginners.
For beginners, installing an air-fuel ratio meter is a worthwhile investment.
FCR Tuning – Changed from MJ(Main jet) 125 to 120 – 2022-06-18【summary】
There is one thing I should reflect on this time. Regarding the MJ exchange, I regret not trying the 138 or 142 before heading home. MJ132 was definitely good, but there was still room for improvement. I feel like I missed an opportunity by going home without testing these sizes.
The next step was to replace the MJ, and it felt like I was just following a straight path without considering other possibilities. I realized that the right approach would have been to either change the jet until it didn’t seem effective or take more time to contemplate the next adjustment.
Perhaps the heat was affecting my judgment. I hope to use this experience in ways beyond tuning.
I wish you a great FCR tuning journey. See you again!
