FCR Tuning – What is the air-fuel ratio at idle?

HONDA CBX1000 air fuel ratio sensor FCR
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FCR Tuning – What is the air-fuel ratio at idle?

As the title suggests, this is about the air-fuel ratio at idle for FCR.
The air-fuel ratio of my CBX1000 at idle is around 13.5 when it's cold.
Once the engine warms up,
it's around 12.9. This is just my current preference.
A senior Z enthusiast says that the air-cooled Z series is 14.
I heard from him that the Z series tends to settle at around 14.0, so I'm still exploring this for the CBX1000 as well.
What I'm going to write about from now on will also include individual differences in air-fuel ratio meters (A/F meters) and the characteristics of each motorcycle.
You should also talk to people who handle a variety of motorcycles.
This will increase the accuracy of the work on your motorcycle.
The information I provide will be less accurate as I only do tuning work on one CBX1000.

There doesn’t seem to be any individual difference between the air-fuel ratio gauge units. It looks like the sensor is used to make the determination.

It appears that the judgement is made by the BOSH sensor, and there does not appear to be any difference between the air-fuel ratio gauge units.
I have replaced only the units three times without replacing the sensor, so this is a reliable estimate.
The air-fuel ratio gauge sensor is vulnerable to overvoltage, so it is a good idea to have it inspected if you have concerns about the regulator system on your motorcycle. I install mine with a converter to step down the voltage.

What is the proper air-fuel ratio at idle for an air-cooled 4-cylinder FCR?

These are just other people's words and I haven't looked into it, so this isn't an accurate account.
A senior Z enthusiast said that there are 14 air-cooled Z series.
Was it when the car is cold? Or after it has warmed up?
I haven't heard the details.
However, since this person tunes a considerable number of cars professionally,
I can trust what he says.

What is the proper air-fuel ratio at idle for an air-cooled 6-cylinder FCR?

When the engine is warm, it is around 12.9.
Even if you change the slow jet from 35 to 52 and tune it until it can be driven normally, it tends to settle at around 12.9.
The sensor of my air-fuel ratio meter may be out of sync, so I don't know if it's the correct number.
I have tried consciously matching it to 14.0 as recommended by experts,
but considering the drop in rotation and ease of starting, I think it's around 12.9.
Recently, I have been tuning the low throttle opening with the instruments, and checking it once or twice during the final test run.
I keep the throttle opening at full closure, 1/16, and 1/8 so that the air-fuel ratio does not change drastically.
Of course, there is a change when idling.
When the acceleration pump is included,
when you look at the numbers on the air-fuel ratio meter, it shows some strange numbers.
I touched the jet thinking that the acceleration pump was not working, so there were times when the strange symptoms continued for a long time.
Pay attention to the discharge timing of the acceleration pump.
It is better to have a leaner air-fuel ratio when idling.
Considering starting in winter, there is no problem with around 12.9.
It is something I keep in mind whenever I tinker with things.
Currently, it is easy to tune it to 12.9 when fully closed.
At low throttle openings, the air-fuel ratio changes drastically even with just a slight twist of the throttle, so I'm not sure what the correct way is.
Is a good balance between fully closed, 1/16, and 1/8 good?
Is it better to have a little lean only when fully closed?
I'm currently trying out various things.
In the process of testing, I keep the fully closed setting at around 12.9,
make starting feel smooth at 1/16,
and when cruising, I'm conscious of being leaner at around 1/8 so that I don't lose the sense of power. I'll keep it in that state if the rotation speed drops well and there is little stumbling when revving the engine.
It's difficult to be completely perfect around full closure, 1/16, and 1/8 as there are many jets to be responsible for,
but I'm currently focusing on 12.9.

I’ve uploaded a video of me revving the bike in the dark on YouTube.


The FCR does not have a choke, it uses an accelerator pump instead.

The starting ritual of an FCR involves twisting the throttle several times.
After discharging the acceleration pump and waiting a moment for the gasoline to evaporate, the engine can be started.
There are FCR models that come with a choke, so in terms of whether a choke is necessary, it probably would have been, but due to design considerations or cost reasons, at least the FCR for the CBX1000 does not come with a choke.

FCR for beginners – The more beginners you are, the more useful the air-fuel ratio gauge is

An air-fuel ratio meter is a beginner's best friend.
Veterans can tune without an air-fuel ratio meter.
Veterans have a wide variety of tools that they can use, and an air-fuel ratio meter is one of them.
Tuning without an air-fuel ratio meter is the same as attempting tuning at a level of difficulty greater than that of a veteran.
Installing an air-fuel ratio meter incurs additional costs.
These include the cost of purchase, installation labor, and the cost of modifying the muffler.
Although welding is required, the hurdle for installation is relatively low.
When it comes to tuning racing carburetors such as FCR,
it is an instrument with extremely high cost performance.
Beginners will be happiest if they install it first.

FCR Tuning – What is the air-fuel ratio at idle?

For me, this is an ongoing topic, but it was about the air-fuel ratio at idle and at low throttle opening. At least in the summer, there is no problem with tuning to 14.0 or the like.
Considering the cold season, I'm thinking about various things, such as an average of 12.9, or settling at around 13.5 only when the throttle is fully closed.
I don't know if the current situation is right or wrong until I try it out a little more.
In the case of the CBX1000, if you keep the air-fuel ratio at around 12.9 at idle, you can start the engine and take off with less stress.
There may be better tuning methods and ideas.
As I write this, I am thinking of tightening the pilot screw and leaning only when the throttle is fully closed.
You may discover something new.
Tuning the FCR is a lot of fun to see what results it produces.
I hope you all enjoy trying out various tunings for the FCR.
See you again!

CBX1000 Photo Gallery

I have selected some photos from previous posts that show the air-fuel ratio meter.
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