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.
When I have a slight concern about FCR tuning, I try to make at least one adjustment. This makes it easier to notice changes, which increases my motivation to dive deeper into tuning. It’s challenging to invest time in something where I can’t determine if there’s a change or not. This time, there are various adjustments I thought of spontaneously. It’s more about fine-tuning than full-fledged tuning, so I’ll write it in a column format.
The FCR tuning is the result of repeated A/B testing. I assess lean and rich conditions multiple times. I’ll explain based on the lean direction. I look for jets that improve in the lean direction and further evaluate whether going leaner yields better results. I repeat this evaluation until I find that the performance worsens compared to before the changes. As a result, I can conclude that the setup before changes was the best.
Since I had a few concerns, I made some fine adjustments. Looking at the air-fuel ratio gauge at low throttle openings, the numbers were showing slightly rich. There are no issues with acceleration or real-world performance, but since it bothered me, I decided to change the straight diameter to lean.
From 90FTX#3 (=90FTM#1) to 90FTN#1.
After a test ride, I felt that it had improved. The air-fuel ratio gauge readings became lean. Going lean can reduce acceleration feel, so I’ll keep an eye on it. I didn’t feel that performance had worsened. I’ll finalize this state and do a longer test ride.
Next, the accelerator pump discharge timing was set at 1.00mm. I changed it from 1.00mm to 2.00mm.
The ride felt significantly better, so I’ll keep the discharge timing at the new setting. If the accelerator pump timing is too early, fuel will hit the throttle valve. The FCR opens the throttle valve very gently up to 1/2 throttle opening.
From my recent tests, I've come to think that tuning the discharge timing is quite labor-intensive. Whether I set the accelerator pump discharge timing adjustment plate at 0.6mm or 1.2mm, it feels like there isn't much difference. So, I settled on a discharge timing of 2.00mm, which occurs just slightly before the throttle valve reaches 1/4 open, and a bit earlier than when it's at 1/2 open.
It seems to have become much easier to ride. However, after only a brief test ride, it’s hard to tell for sure. Since the rider's perception and the weather can change from day to day, the results might not be very reliable. I decided to keep it flexible for future adjustments.
This is more of a fine-tuning rather than a full tuning process. It involves minor adjustments that don't take much time.
For FCR Beginners – Adjusting the Acceleration Pump Timing is Relatively Easy.
If possible, please purchase a thickness gauge. Document how the motorcycle changes with tuning the acceleration pump timing. This also helps develop the habit of keeping a work history and practicing. Adjusting the acceleration pump can dramatically improve the motorcycle's performance. Enjoying the acceleration feel of the FCR is one of the great pleasures of tuning.
The acceleration pump can significantly change how the motorcycle runs, either positively or negatively, especially if its timing is set too low. In my subjective experience, when the timing is set at low throttle openings, it often feels harder to ride. I believe the acceleration pump should be viewed more as a seasoning for when the throttle is opened quickly, rather than a core component of tuning. This is just my current perspective, and it may change over time. However, I've often found that making extreme changes to the acceleration pump has led to substantial improvements.
Was the acceleration pump a hindrance? Or was the timing simply set correctly? I haven't validated this, but regardless, I currently cannot incorporate the acceleration pump into my tuning adjustments effectively. This blog post may feel a bit sparse in content. When I work on motorcycles, I try to write something down, as I think it might be helpful for readers.
Spring and autumn in Japan are enjoyable times for tuning FCRs. Please be cautious of accidents and ensure safe riding and proper gear during your test rides. See you again!
CBX1000 – Working photos
Work Photos for CBX1000
Even if you don’t have a thickness gauge, if you have an object of known thickness, you can still make adjustments to the accelerator pump discharge timing plate. For adjustments close to the optimal value, a 0.2mm change is noticeable. Anyone who has adjusted it at least once knows that achieving high precision can be challenging.
My CBX1000 has two accelerator pumps. I carefully measure and adjust to ensure their timings do not get misaligned. The reason I used a coin is that I wanted to test opening the plate width more significantly.
