FCR tuning – If you make the jet needle straight diameter lean, it may be pointless to make the jet rich…

HONDA CBX1000 - FCR tuning FCR
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FCR tuning – If you make the jet needle straight diameter lean, it may be pointless to make the jet rich…

This is a description from the history of CBX1000 FCR tuning.
Intentionally disrupting the jet balance can also make it possible to use jets that cannot be used. The CBX1000 has a tendency to have insufficient clip stages for lean.
It is a technique to drastically change the straight diameter of the jet needle to lean in order to compensate for insufficient clip stages.
If you look at the tuning manual, the range of influence of each jet is described.
The percentage of how much the air-fuel ratio will change when you change it one step from the current number is described in +-15%.
If you read it based on the assumption that it will always change by 15% as shown in the graph, changing the current number by two will not change by 30%, but by 32.5%. Changing it by three will change it by 52.0875%.
It is a quadratic curve, so the change is not exact. It is a slightly more accurate way of thinking than the idea that it is simply proportional in 15% increments.
It may be fine to think of it as roughly changing by one number.

Changing one jet also has an effect on others.
The range of influence of each jet overlaps to some extent, but the ranges are slightly different.

Normally, changing one jet will only change that one jet.
For example, when the throttle is about 1/2 open, the combination of the straight diameter of the jet needle and the main jet determines the air-fuel ratio.
5 + 5 = 10
3 + 7 = 10
Both values ​​will be 10.
If you change the jet needle number to lean and the main jet number to rich,
the result is the same.
The ranges of influence are slightly different, so the air-fuel ratio will be the same at 1/2 throttle opening, but there will be slight changes at other throttle openings.

Last year, the straight diameter of the jet needle was mainly set to [R].
Currently, it is mainly set to [M].
When it was set to [R], the slow jet was set to a larger number and the main jet was set to a larger number.
On the other hand, when changing from [R] to [M], the slow jet and main jet were also lowered.
The jet needle and main jet are rods and holes, so it is natural that the air-fuel ratio is determined by their mutual combination.
The tuning changes with the thickness of the jet needle. In short, tuning is a balance, so even if you change one place, they will affect each other.
If you change two places, you can deal with the cut-off to some extent even if the clip stage is insufficient. The theory when tuning is to change one place at a time.
If you change two places, the tuning will change overall, so if you're not careful, you may end up with almost no change.
If you have a somewhat fixed idea, the straight diameter of the jet needle is based on [M] and is considered lean or rich.
The main jet is not a single main jet, but has a partner called the main air jet. The tuning manual says that it is okay not to change it because it is not very effective. At low throttle openings, various parts such as the straight diameter, clip stage, taper, slow jet, and air screw are intertwined. There are many cases where changing two places will result in less change than changing one place. The point is whether to change two places at the same time to make the desired change. In my case, I felt that the number of clip stages was insufficient, so I changed the straight diameter from [M] to [R]. Since the jet needle became lean, the slow jet should have been rich, but I did not change it. I tried changing the slow jet many times. In the end, when I asked BITO, they were selling a jet needle with a straight diameter of [M] that changed the cut-off, so I went back to the basic tuning of [M]. In the end, even if I changed the straight diameter, the number of clip stages was about 1 step for the straight diameter 3rd. In the end, whether the FCR is large body or small body,
the slow jet is [38]-[48]
and the straight diameter is [M] as a standard.
The main jet should be in the range of [115]-[140]
or it will be a balance that does not address tuning of the parts that concern you.
If the slow jet size is set to 60, the jet needle should be between 90FTU and 90FTX. The clip number can also be changed to rich.
Even so, the balance does not change, so there is not much change in terms of driving.
Since the FCR is not digital, there may be some changes that are quite bad in the parts that affect each other. Of course, the main jet should also be set to a large size of about 160 and not use all the jets that were installed at the factory.

When tuning, consider the slow jet or jet needle as the basis.

FCR is rarely changed significantly from the time of shipment.
When I asked BITO about the CBX1000, they told me that they had changed the jet needle three times.
They were probably thinking of keeping the slow jet within the range of 40 to 48 and allowing for a range of clip adjustments. The jet needle is 90FXM and has a unique cut-up.
If you use the jet needle you want to use as your main as a reference, the method is to change the slow jet and main jet together. As for the main jet, the only tuning range available at full throttle is the main air jet, so some compromises may be necessary at full throttle.

FCR for beginners – Keep a good record of tuning history

The content of this blog post is written based on your history.
There are some things you wouldn't notice unless you look at your history.
And since I was a beginner, I have been recording my history in my own way, in a Google spreadsheet. Leaving a history is something that can be done by anyone, whether you're a beginner or a veteran.
Naturally, veterans will leave a more accurate and easy-to-understand history.
Even beginners can leave a history. Photos of you working are fine too.
Leaving a history is always useful. Please try to be conscious of it.

FCR tuning – If you make the jet needle straight diameter lean, it may be pointless to make the jet rich…【summary】

I imagine that the appropriate jet for the CBX1000 would be around 90FTS#1 to 90FTS#3, with a slow jet of 55 and a main jet of around 135. There was a time when I actually tuned it like that. After that, I changed to a 90FXM jet needle and tuned it. It feels a bit awkward because I can't adjust the straight diameter by one number, but I can adjust the clip number all year round without worrying too much.
I'm currently tuning my CBX1000 with 90FTN#1 because I wanted to adjust the straight diameter.
I'm planning on retuning it with 90FTS this summer, or trying 90GTM.
I hope you all have a fun FCR life.
See you again!

CBX1000 Photo Gallery

Here are some photos from previous posts showing the engine and FCR.
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