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 – An Easy Way to Turn Off the Accelerator Pump
You can clip the pushrod of the accelerator pump to stop it from moving. That's all there is to it. I will also add some photos, so please check them for the size and the position where you should clip it.
For those using the old model FCR on a CBX1000, there are two reference carburetors. I think you need to remove the carburetors to reach them, but if you have small hands, you might be able to reach without removing them.
I will write notes and column-like text after explaining the photos.
Photo of Turning Off the Accelerator Pump with a Clip
The size of the clip is about 19mm x 9.5mm. Lift the rod of the accelerator pump and fix it in place with the clip so that the accelerator pump does not move. Turn the throttle to make sure it does not come off. You cannot control the total amount or timing of the accelerator pump's discharge. However, you can completely turn it off.
It doesn’t have to be a clip; as long as the pushrod doesn’t move, anything will work. The clip size mentioned is just an example, so it’s okay if it’s a bit larger or smaller as long as it meets the requirement of preventing the pushrod from moving.
The conclusion on whether the accelerator pump is necessary for the FCR tends to be controversial, and there’s no definitive answer. Logically, it seems necessary. The FCR's acceleration pump can feel a bit unwieldy to control, but I’d prefer to use one.
The purpose of the accelerator pump is to supply a burst of fuel to compensate for the increase in air when the throttle is opened. This helps address the lean condition that occurs as more air is drawn in. Since the carburetor operates based on the engine's suction power, it can become leaner depending on how the throttle is opened, and the accelerator pump helps to counteract this.
Although it’s a useful feature, the mechanism can be somewhat crude. Unfortunately, we have to accept this as a characteristic of a less refined system. Despite its shortcomings, I want to make the most of this valuable feature.
For FCR Beginners – How to Understand the Effectiveness of the Accelerator Pump
Since the accelerator pump can interfere during tuning, I reduce its total discharge amount. Once tuning is complete, it's also a good idea to turn it off and then turn the accelerator pump back on. However, since the tuning assumes the presence of an accelerator pump, I adjust the total discharge volume accordingly and generally avoid making many changes.
If the discharge timing is too fast, the fuel may hit the throttle valve directly. In my CBX1000, even with a 1.6mm timing, it sometimes causes this issue. Currently, I have it set to 2.3mm.
This is an easily adjustable part, so if you’re interested, try experimenting with different settings or toggling it on and off to see how it affects performance. This also ties into the concepts of acceleration and partial throttle, so exploring various settings might be beneficial.
This feature is more crucial from half-open to full-open throttle rather than at low throttle openings. The FCR is a racing carburetor, not a standard carburetor.
If you’re looking for better rideability at low throttle openings, consider adjusting the fuel to be slightly richer or tightening the air screw. For precise control at low throttle openings, relying on functions like the accelerator pump isn’t ideal.
FCR Tuning – An Easy Way to Turn Off the Accelerator Pump【summary】
You can determine whether your motorcycle needs an accelerator pump by comparing its performance with the pump on and off. Check the difference in acceleration, especially when opening the throttle suddenly from 1/8 to 1/2. From my experience, it doesn’t seem necessary for about 1/4 throttle opening. Currently, I try to adjust the fuel discharge so it doesn’t hit the throttle valve directly.
I’ve been experimenting with various settings by replacing the accelerator pump diaphragm to find the optimal total discharge amount. Each change makes a difference, and it’s challenging to determine the best setting.
The FCR’s accelerator pump seems less refined compared to the TMR. FCR was an evolutionary improvement from the CRS carburetor. I’ll make the most of this feature and enjoy motorcycling.
I hope you all have a great experience with your FCR.
