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 – Slow jet changed from 48 to 55 – 2022-05-23
I changed the FCR's slow jet (SJ) from SJ-48 to SJ-55.
As intended, I adjusted P1 by turning it back 15 minutes return. The goal is to bring the air screw (AS) adjustment back to around 1.0 to 1.30 minutes return. Since I also had an SJ-52, I decided to go with at least an SJ-55. I don't expect the AS to be at around 1.30 minutes return, so I increased the jet size all at once.
I don't have any photos of the work in progress this time, but I removed the float chamber when replacing the slow jet (SJ). This is the part at the bottom of the FCR where gasoline accumulates. Gasoline leaked from the gasket between the main body and the float chamber. Be careful when tilting the carburetor or removing the float chamber, as these types of issues are likely to occur.
I replaced the gasket, and because it was in poor condition, I immediately discarded it to avoid reusing it.
It's something I learned from the internet or read somewhere. Regarding FCR tuning, it's said that the air screw (AS) can be set to 1.0 to 1.30 minutes return, and in many cases, this seems to produce the best results. So I wanted to try it out and adjusted the count to the extreme.
It’s often recommended to increase the rotation speed for each cylinder individually to find the best setting, but my CBX1000 has two stop screws, and even when I tried tuning each cylinder separately, I couldn’t get it quite right. So, I’m generally counting on the overall settings.
The return of the AS is based on two factors: a smooth clutch engagement and no extreme drop in power at 1/8 throttle opening. While not in neutral, I tested it a bit by starting on a hill to gauge the power feel when taking off. I've adjusted it to open as much as possible.
If the AS is opened too much, it can lead to a sparse feeling with no sense of power within the AS's range.
How has it changed?
There were no major changes in the tuning before and after the adjustments mentioned above. While there were some subtle differences, it doesn't seem to have made things noticeably better or worse. Since this might impact the needle jet's (JN) performance range, I'll try switching the JN from 90FTR to 90FTS and see how it goes.
For FCR beginners – AS tunings
The return of the air screw (AS) ensures that power doesn’t become sparse when starting, and I bring the AS back to the limit when making adjustments. I use this approach when tuning the AS.
Make sure the vehicle can take off smoothly with the throttle opening from clutch engagement to about 1/8. I use this as a guideline.
Therefore, when I really want to make fine adjustments, I try to restore the pilot screw (PS). When driving, the throttle might not open even 1/4 while cruising, but it could be around 1/8, so it’s better to fine-tune it to a certain extent to match your preferences.
as renge
ps renge
It's easier to visualize it if you check the range.
FCR Tuning – Slow jet changed from 48 to 55 – 2022-05-23【summary】
Regarding the SJ replacement, if you only look at the part where the SJ was changed, there isn’t much of an issue as there’s little noticeable difference. Overall, the FCR tuning is in good condition, with the AS staying around 1.30 minutes return, which tends to result in many positive outcomes.
However, with the CBX1000, it might end up feeling less interesting to me. A while ago, the combination of SJ-52 and JN-90FTS worked very well. There are also specific needle jets (JN) that pair better with each SJ.
For example, the combination of SJ-52 and JN-90FTR seems better than SJ-52 and JN-90FTS. Similarly, the combinations of SJ-48 with JN-90FTS and SJ-48 with JN-90FTR seem more favorable. This could be due to imagination or seasonality, but it’s an experience worth having.
After repeating the procedure many times, you might realize that the vacuum gauge needle was incorrectly calibrated. I hope everyone enjoys their FCR tuning journey.
