FCR Tuning – Look at the air-fuel ratio during acceleration, not partial

6 series FCR carburetor FCR
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FCR Tuning – Look at the air-fuel ratio during acceleration, not partial

Looking back on this year, there are some things I pay attention to when tuning the CBX1000 FCR that are different from 2021.
I try not to look at the air-fuel ratio in partial.
Partial means a stable driving state with the throttle fixed.
The following post is written assuming that an air-fuel ratio meter is installed.
It may not be very meaningful to get an air-fuel ratio of 12.5 or so in partial.
Since the engine is always running, it is difficult to say for sure, but
I try to get numbers such as 12.5 to 13.0 quickly during acceleration, and place importance on the feeling of acceleration when twisting the throttle. The carburetor sucks in more air when the throttle is opened.
The carburetor uses the force of sucking in air when the piston goes down to atomize the gasoline.
For just the moment that air is sucked in, the air-fuel ratio goes lean.
Then I check to see if the number moves to rich and accelerates smoothly.
By the way, if the acceleration pump is too effective, the moment you open the throttle,
the air-fuel ratio will move toward rich and lean. If the acceleration pump is too effective and the air-fuel ratio moves toward rich,
it will take a while for the engine to accelerate. This completely defeats the purpose of a forced opening and closing carburetor,
whose advantage is that it responds quickly to the throttle.
It is difficult to see the air-fuel ratio accurately during acceleration, but you can get a feel for how the numbers are moving.

Can you tell by the color of the plugs?

It is difficult to determine tuning by the burnt color of plugs.
It is correct to look at the burnt color as a reference.
The burnt color of plugs can only tell you a rough idea.
Carburetor structure is complex.
In the case of an FCR, there are three types of jets that can be changed: slow jet, jet needle, and main jet. Each jet has a different throttle opening. The CBX1000 has six cylinders.
There is also some variation between each cylinder.
It is not realistic to tune by the burnt color of plugs.
It is only a reference if you want to check the condition of the carburetor.

Is it possible to tune by relying on your senses?

Measuring the quality of tuning by feel alone may be the right way to do it.
In the days before air-fuel ratio meters and chassis dynamos, I tuned by feel.
I don't tune with someone directly teaching me how to do it.
When something seems strange, I look at the instruments.
It's my feel that something is strange.
There's no problem with tuning by prioritizing feel.
If you have an air-fuel ratio meter, you can immediately tell if something is strange and it's rich or lean.
Nowadays, you can tune by feel.
Sometimes it's hard to tell clearly whether it's lean or rich.
Sometimes I have a preconceived notion that I should change the jet to the lean side, but I change it to the rich side.
Tuning by feel only goes as far as the parts that feel strange.
The tuning that you feel is good based on your own feel is likely to be the best.
Conversely, tuning based only on numbers may not provide a sense of acceleration.
It's best to tune by both feel and the air-fuel ratio meter.

For FCR beginners – Rich has a better acceleration feeling when tuning

The premise is that you start from a state where pre-tuning is mostly done, and you are concerned about tuning, but can still enjoy riding.
It also depends on your riding style and throttle operation.
I think that a feeling of a little rich gives a sense of acceleration and power. Even if you tune it when it feels rich, the tuning is often very good. If it is blowing black smoke or there is a bumpy feeling, it is too rich. Also, if it revs well but there is no sense of power, it is too lean. If the motorcycle is going at a fair speed when it is too lean at about 1/2 throttle opening, it is often hard to notice. If you don't feel a bumpy feeling but the acceleration is a bit iffy, it is too lean. When tuning, if you start from a point where it is too rich and not running well at each throttle opening, you will not end up in a state of too lean.
In terms of the jet needle clip step, try lowering it until you can no longer ride rich.
From there, raise the clip one step at a time in the lean direction.
You should find the clip step that works best for you. You should decide the clip number based on your own preference rather than on the air-fuel ratio.
I have the impression that leaner gives better revs and acceleration, but initially it's best to tune it to something a little rich. My current preference is to tune it a little rich.

FCR Tuning – Look at the air-fuel ratio during acceleration, not partial【summary】

In this post, I use a lot of keywords like "rich" and "lean".
"Rich" and "lean" are used when there is something to compare them to.
In my opinion, the definitions of rich and lean are roughly as follows.

"Rich" without a comparison is around 12.
"Lean" without a comparison is around 14.
"Too rich" is 10 or less.
"Too lean" is 15 or more.

It depends on the time, place, and occasion.
The appropriate air-fuel ratio also changes depending on the type of motorcycle and the tuning of the engine.

My favorite tuning these days is when the air-fuel ratio is 12.5 to 13 while accelerating.
I used to check the air-fuel ratio in partial, but it was a very fuel-efficient model,
and although it would accelerate, it would not be able to keep up with other motorcycles.
It is important to compare with other motorcycles.
I hope you all have a fun FCR life!
See you again!

CBX1000 Image Gallery

These are photos of the tuning process. You can easily attach/detach the carburetor and sync it outdoors.
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