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.
Will fuel efficiency improve if I switch from a normal carburetor to an FCR carburetor?
This is about whether the fuel efficiency of a motorcycle will improve by installing racing carburetors like the FCR. I will write this in a column format. I have previously written similar articles, briefly discussing whether fuel efficiency improves. This time, I will write with the straightforward title of whether fuel efficiency improves. There may be a lot of overlapping content with past blog posts. So, let’s get started!
The differences between normal carburetors and racing carburetors
The mechanisms of normal carburetors (vacuum type) and racing carburetors (mechanical slide type) are fundamentally different. The FCR is a racing carburetor. It's not that mechanical slide carburetors are inherently better just because they are racing carburetors; it's simply a difference in mechanism. Mechanical slide carburetors are designed in a way that makes them more suitable for racing. They also have the advantage of being easier to tune.
A normal vacuum-type carburetor adjusts the air-fuel mixture by lifting a diaphragm with the airflow when the throttle is opened. This mechanism uses the power of the air, creating some automatic adjustments. This significant difference means that the use of air can result in a slight delay in throttle response, making it less suitable for precise carburetor tuning.
Regarding the delayed throttle response, it’s debatable how noticeable this is to a human, and how effective a fraction of a second can be is also subjective. In racing, where milliseconds matter, this is an important consideration. However, the critical point is that precise tuning is difficult with vacuum-type carburetors.
One of the main goals of racing carburetors is to achieve ideal tuning.
Can tuning an FCR improve fuel efficiency?
I have also installed an FCR and done various tuning, so I haven’t completely ignored fuel efficiency. Regarding my thoughts on fuel efficiency:
It is possible to intentionally tune for better fuel efficiency by increasing the lean area or turning off the accelerator pump. However, this can lead to a lack of acceleration and other drawbacks.
Opinions vary on whether fuel efficiency increases or decreases with an FCR. If fuel efficiency improves after switching from a vacuum-type carburetor to an FCR, it could be due to poor tuning or maintenance of the vacuum-type carburetor.
In the past, although not intentionally, I ended up with a tuning focused on improving fuel efficiency. I tuned it to maintain an air-fuel ratio of around 13.5 at various throttle openings, and around 12.9 during acceleration. As a result, fuel efficiency improved, but the power feel and acceleration when opening the throttle were quite poor. At that time, I did not notice the lack of acceleration, but it felt somewhat disappointing with an FCR that didn’t accelerate quickly when twisting the throttle.
Fuel efficiency improvements with an FCR are greatly influenced by riding style.
Whether fuel efficiency improves with an FCR is primarily influenced by riding style. I believe that for a motorcycle with an FCR, riding in a way that avoids raising the oil temperature too much is beneficial for fuel efficiency. The goal with a racing carburetor is not fuel efficiency but the best air-fuel ratio.
The ideal air-fuel ratio for a power-rich state is around 12.5, while for complete combustion, it is 14.7. Currently, when tuning, I aim for the air-fuel ratio to be between 12.0 and 13.0 during acceleration. At partial throttle, it tends to be rich.
Complete combustion can lead to lean conditions during sudden engine braking or acceleration. Tuning lean doesn’t necessarily result in significant improvements. In my view, the rider’s riding style plays a major role in fuel efficiency.
Will fuel efficiency improve if I switch from a normal carburetor to an FCR carburetor?【summary】
My conclusion is as follows:
It is unclear whether fuel efficiency will improve simply by switching to an FCR. Fuel efficiency is influenced by riding style. Vacuum-type carburetors might generally maintain a more appropriate air-fuel ratio. The FCR can potentially be tuned to achieve improved fuel efficiency intentionally. This is my summary. I can’t continue to pursue fuel efficiency with an FCR. See you again!
CBX1000 – Photo Gallery
We will post excerpts from past posts, mainly photos of FCR.
