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 – Adjust the throttle return and turn the pilot screw
Added on 2024/02/14:
I wrote this post when I didn’t have a carburetor adjustment tool. In reality, the changes in the pilot screw (PS) are noticeable.
The idle speed suddenly jumped from idle to 1/8 throttle, so I adjusted both the PS pilot screw and the air screw (AS). I’ve been pondering this for a while, but it’s difficult to determine if the PS pilot screw adjustment is effective. The change might be a placebo effect, so I adjust it just in case.
By the way, regarding the notation of the screw adjustments, "minutes" is used as a reference to the position of a clock hand, divided into 60 parts:
・PS 1.00 and AS 0.35 minutes ・PS 1.30 minutes and AS 0.45 minutes
Comparing this with the amounts recorded in the video, I feel that the return is slightly improved. I tested the settings, and the progression was:
There was no extreme richness or lean condition between these settings. It doesn’t seem to lack power.
Though it may not be significant, I’m considering changing the slow jet (SJ) to 48 or 50 and opening the AS air screw a bit more.
I’m unsure if the meter is affecting the return to idling, if it’s due to the tuning, or if it’s related to the deterioration of the FCR. When I was tuning, there were times when the return was very slow, so I plan to adjust the tuning again, keeping in mind that tuning might need further adjustments.
CBX1000 FCR response return – with images and videos
PS Pilot Screw Adjustment – caburetor adjustment tool
I use a carburetor driver for adjusting the PS pilot screw. However, the adjustment tool often separates from the screw during the process, likely because the carb driver isn’t properly engaged with the PS pilot screw. This frequent separation means I often have to remove and reinstall the carburetor to check the return rotation speed of the PS pilot screw. Unfortunately, this renders the tool less effective.
Currently, I stop the engine to adjust the PS pilot screw, but I’d prefer to be able to make these adjustments while the engine is running. Unfortunately, this is not yet feasible.
FCR Tuning – Adjust the throttle return and turn the pilot screw【summary】
As mentioned earlier, I am still not able to fully experience the effects of the PS pilot screw adjustment. It might be a placebo effect when I notice a change after adjusting the PS pilot screw. Additionally, my CBX1000 might be experiencing issues with the PS pilot screw.
In any case, the fundamental approach is to return to the baseline setting of 1.0 and proceed with the tunings. If the SJ (slow jet) is increased, the AS (air screw) can also be opened wider. Therefore, I plan to change the SJ from 45 to 48 or 50 next time and check the tuning for low openings.
At present, I believe the reason the engine momentarily stalls when returning the throttle is due to a significant difference in the air-fuel ratio across throttle openings from idling to 1/16 and 1/8. I hope to find a satisfying answer, but if not, I'll try not to dwell on it too much since I’m still in the process of running it.
FCR tunings are not recorded on paper but are uploaded to the cloud along with the date. I save them on my smartphone for quick reference. I use Google Cloud Spreadsheets for this purpose.
Regarding the PS pilot screw, simply opening and closing it affects the air-fuel ratio from idling with the throttle fully closed to slightly opening the throttle. For the CBX1000, while it was previously unclear if the PS pilot screw was effective, it is quite effective. However, there are cases where the PS pilot screw does not function as intended.
The carburetor adjustment tool is compatible with the CBX1000. You can now clearly observe the air-fuel ratio while the engine is running. The PS pilot screw may not work if the SJ is too large or if the idling stop screw is set too high; the engine can idle even when the screw is fully closed. This issue likely relates to the idle port and slow port.
It would be beneficial to verify the return using a new carburetor and a new meter, though it seems unlikely that an amateur DIY approach will achieve that quickly. There is a possibility that I might purchase another FCR, so I would like to compare the old and new ones.
