About FCR-PS. Idle port, slow port and air-fuel ratio at idling

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About FCR-PS. Idle port, slow port and air-fuel ratio at idling

The other day, when I was carrying around a Carburetor pilot screw adjustment tool, a certain mass touring group contacted me.
"What is this? ”
I was bombarded with questions in turn.
I was able to come to my own conclusion about things that I had doubts about since I started tuning up FCR,
I've done it before, so I'll write about it historically.
my own way
I am writing about my thoughts. There may be differences from articles written in the past.
Maybe it's evolving day by day. Since I am not familiar with FCR tunings,
Your way of thinking may change from time to time.
Please understand that I may have written something incorrectly.

There is a clear difference between an idle port and a slow port.

Please take a look at the photos first. The slow port hardly shows its face when the throttle valve is closed. By the way, does the idle port and slow port switch depending on the throttle valve opening? Does it overlap? This is a part that is unclear to me. I would like to know more about how it works.
スローポート = slow port
アイドルポート = idle port
エンジン側 =engine side

The low opening degree of FCR has many areas where they influence each other.

SJ slow jet, AS air screw, PS pilot screw, JN jet needle straight diameter
There are many factors that interact with the number of JN jet needle clip stages. Once I have decided on SJ and JN, I set them up so that AS and PS balance out the best conditions.
It's like determining a rough range with SJ and JN, and making fine adjustments with AS and PS.
Without looking at the PS, if the AS does not fall within the range of the lower limit of screw return of 0.30 minutes to the upper limit of return of 2.30 minutes, change the SJ count and readjust.

What do you do with the PS pilot screw?

This is when it is fully closed. It may depend on the influence of SJ and other jets, but it is difficult to bring the air-fuel ratio to the expected value just by tuning the PS. A small change will not cause a large change in the air-fuel ratio value.
Even if the PS is fully closed, it will idle fine depending on the height adjustment of the stop screw and the size of the SJ. For me, PS is an adjustment to maintain starting performance and idling when cold.
In order to keep the engine idling stably, it is also necessary to adjust the lower limit of the throttle valve height at idling using the stop screw.
If you select SJ with only the PS return at idle in mind, problems will occur at other throttle openings, so
You may have to compromise to a certain extent than your idea of perfection.

Air fuel ratio at idling

In the routine of starting and accelerating the motorcycle, when I set it to what I thought was a good condition, it was around 11.9. Recently, it has settled down to around 14.5.
This tends to be largely determined by the number of clip stages.
The clip was quite low when it was about 11.9 when fully closed.
When it is fully closed and it is about 14.5, the number of clip stages is above the level where the cut-up is changed.
I'm not sure which air-fuel ratio is best when fully closed, but my current preferred tuning is around 14.5. Also, according to a professional who has set up many cars, the air-fuel ratio when idling is around 15, so I wonder why when the air-fuel ratio was around 11.9. I thought,
I think that the cause was the number of clip stages on the JN.
The reason why he is currently tuning the clip level higher is that after playing around with the JN with the theme of being able to ride comfortably when using a high throttle and making the throttle work a little sloppy, he felt that he liked the feeling when he set the clip level higher. This is the result. When the throttle is fully closed, there should be no stress on the three points of cold startability, idling, and clutch engagement, but when starting at a low opening, it will be around 13, even if there is a load on the rear wheels. It is necessary to use AS to adjust the air-fuel ratio to give a sense of power.
In this respect, each tuning influences each other when it comes to low opening degrees.

For FCR beginners – Air-fuel ratio meter installation

The biggest problem with FCR tunings is whether the tunings are deep or thin. Just rely on your senses
It's an unclear place. There is no way that an amateur who has just started using racing carburetors such as FCR can make such judgments. Veterans who have been tuning carburetors since the days when air-fuel ratio meters were expensive can judge the best engine speed just by feeling, and that's because they have experience.
On the other hand, troubleshooting by a beginner who can provide numerical values may be more reliable than troubleshooting by a veteran who cannot provide numerical values. It is not necessary to use an air-fuel ratio meter for the first time, but we recommend equipping it at an early stage. Even amateurs will be able to set the lowest line based on numerical values if they take the time. Veterans simply reach the passing mark faster than amateurs. It may be impossible to reach the best tuning, but you will be able to get close to the best tuning. The provision of an air-fuel ratio meter is one of the modern trends. For those who are about to start tuning up FCR, we recommend early equipment.

About FCR-PS. Idle port, slow port and air-fuel ratio at idling【summary】

I try to touch on FCR when I'm interested. The reason why books on FCR tunings have not been published is because the systematic optimal solution is unclear.
There are various ways of thinking about the best air-fuel ratio when idling, like this time.
I'm not sure if I'm writing correctly or not.
This applies to CBX, but it may not apply to SR.
There's no answer to how to do it, but if you've done similar things on similar motorcycles, you should be able to get some guidelines. The hot days are still continuing, but everyone please take care of your health.
Please enjoy your FCR life.
See you again!
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