FCR Tuning – Regularly resetting the air screw and pilot screw can improve performance.

FCR Tuning – Regularly resetting the air screw and pilot screw can improve performance.

The FCR air screw and pilot screw are parts that can be adjusted continuously. The slow jet and main jet needle can only be adjusted with specific sizes. In particular, the air screw is easily accessible once you remove the filter or funnel. This makes it straightforward to observe the changes related to tuning. The frequency of adjustments for the air screw varies from person to person, depending on the riding conditions or seasons.

When you adjust by opening or closing it by 0.15 turns, you may lose track of how far you've turned it back from being fully closed. (Note: I use clock notation; 1.15 turns means one full turn plus 90 degrees.) Make sure to take thorough notes when tuning.

If you're adjusting while the FCR is still mounted on the bike, you might experience significant discrepancies between cylinder 1 and cylinder 6. My CBX1000 requires frequent adjustments, and there has been a noticeable discrepancy between each cylinder, generally around 0.10 turns. The CBX1000 has six cylinders. While a 10-minute discrepancy may not seem like a big deal, it can be psychologically unsettling.

When the adjustment differences between cylinders become significant, I close the air screws completely and then adjust all cylinders back to the same position. Performing this task often results in a dramatic improvement in RPM response and overall performance. In my recent tuning, I adjusted all cylinders to 1.30 turns back.

The manual suggests finding the point where the engine RPM increases for the air screw for each cylinder. However, it's difficult to measure RPM on the CBX1000. With my current tuning skills, I can't reliably determine the RPM increase for each cylinder, so I set them all to the same adjustment.

I encourage you all to occasionally reset the FCR air screw and retune. That’s all I wanted to write about this time. Since there isn't much content, I'll dig deeper into it.

Now, let’s get started!

There is a part called the slow air jet.

Regarding the air screw, there is a part called the slow air jet.
Originally, the slow air jet was more widely used first. However, since the development of the slow air screw, it seems to have fallen out of common use.
If you want to adjust the air intake accurately, the slow air jet is a fantastic option.
Considering the costs of obtaining different sizes and the time involved, most people conclude that using the air screw is the better choice.
I want to try tuning multiple times. If there's a significant difference in the time required for items that have the same effect, the slow air jet becomes impractical.

※In Japan, it used to be possible to order various sizes of slow air jets from KIJIMA with quick delivery. However, as of October 2023, it’s unclear whether they can be ordered immediately. Online, it appears they are now special-order items. While delivery may take a while, the chances of obtaining them are relatively high.

After adjusting the air screw multiple times, you should also re-synchronize the carbs.

It all comes down to your perspective on carb synchronization.
After repeatedly adjusting the air screw, you should re-synchronize the carbs. There is usually a slight misalignment.
However, since it’s not a major shift, you can re-sync the carbs quickly.
Carb synchronization affects how the throttle returns.
If the synchronization is only slightly off, it won’t cause any major issues while riding.
However, if it’s significantly misaligned, the engine speed may not drop easily.
When the synchronization is largely off, adjustment is necessary.
A properly synchronized carburetor provides a satisfying experience when idling or revving.
If you're doing DIY tuning on your FCR carbs, I highly recommend paying close attention to synchronization.
It will surely make riding your motorcycle even more enjoyable.

FCR初心者向け-エアスクリューの調整をしてみる

Anyone can adjust the air screw by simply turning it.
However, beginners might feel hesitant to touch it. Here are a few points to keep in mind:

＠Running without the power filter or funnel is not an issue.

・While it’s not an absolute rule, as long as you are cautious and avoid large debris entering the engine in a short time, there shouldn’t be any problems.
・For the FCR, you want to avoid even small sand particles getting around the float valve, as this could damage the carburetor body.

＠Whether you have filters or not, tuning will hardly change.
・Installing or removing the funnel or filters doesn’t cause significant changes to the air-fuel ratio. However, you may notice a difference in throttle response when opening the throttle.

＠The smallest way to turn the air screw.
・I adjust the air screw in increments of 6 degrees, or in terms of a clock face, 0.05 minutes, ensuring all cylinders are adjusted equally. It’s not like tuning a musical instrument, where even a sub-millimeter adjustment can lead to a dramatic change.

＠Should the air screw be adjusted differently for each cylinder?
・For my CBX1000, the point at which idle increases varies by no more than 0.15 minutes across cylinders. I adjust them all equally, using an averaging approach. Adjust in increments of at least 5 minutes; do not attempt to adjust continuously without clear steps.

＠Use a dedicated screwdriver to turn the air screw.
・The air screw has a brass flathead. Using a flathead screwdriver that doesn’t fit properly could strip the head, so be careful.


These are the points to be mindful of.
While I mentioned adjusting the air screw with a precision of 0.05 minutes, it’s okay to make adjustments in increments of 0.03 minutes as well.
Always keep a record of your tuning. When turning the screws, keep in mind that it should be easy to log numerical values. If you don’t do this, you might encounter trouble later, like being unable to read past tuning records properly when you make adjustments again a few months later.

FCR Tuning – Regularly resetting the air screw and pilot screw can improve performance.【summary】

Both the air screw and pilot screw can be adjusted continuously without fixed increments.
The tuning manual only specifies the lower and upper limits. Even if you go slightly over these limits, the engine won't be damaged.
When using 3.00 minutes return the baseline, small adjustments are hard to notice. However, when using 0.15 minutes return as the baseline, small adjustments can result in overly large changes.
What’s important is being aware of both the relative change, which shows how much adjustment was made from the current tuning, and the absolute change, which indicates how much adjustment was made from fully closed.
When recording work history, it’s essential to note the absolute values; otherwise, it becomes difficult to explain to others or even understand yourself the next time you make adjustments.
Unlike jets, screws can be adjusted continuously, so without setting a minimum movement range, you can’t effectively apply the tuning in the future.
Personally, I have set the minimum adjustment precision to about 0.05 minutes return of a turn, like the movement of a clock hand.
If you adjust the screws repeatedly in relative terms, the screw position can gradually deviate from where you originally intended.
To address this, it’s occasionally necessary to reset the screw position and re-tune the system.
This blog post was about the periodic resetting of air screws and pilot screws.
See you again!

CBX1000-Related Photos

I remove the Foam Air Filter Sock while tuning.
When resetting the air screw, I do it in a direct carburetor state. The reason is that when the Velocity Stack is installed, it becomes difficult to turn the screw accurately. There are advantages, such as applying equal force, keeping the driver angle consistent, and making it easier to visually check.
The disadvantage is that the process of attaching and detaching takes more effort. Since the purpose is to reset, it’s meaningless if I can’t thoroughly check it.
I frequently adjust the FCR. About once a month, I perform these tasks, including synchronization.