FCR Tuning – Full throttle! Check the main jet for each gear

FCR-メインジェット FCR
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FCR Tuning – Full throttle! Check the main jet for each gear

This is my own method of tuning the main jet of the CBX1000 FCR.
I'll use a chassis dynamometer.
This will be written in a slightly abstract way.
First of all, it is assumed that the tuning has been done neatly up to 3/4 throttle opening.
If the throttle opening is about 1/2, you can see the change even if you change the main jet by about 2 numbers from 120 to 125.
At about 1/2 throttle opening, the straight diameter of the jet needle and the number of clip stages are also involved in a complex manner. Changing any of them will have an effect.
If the main jet is lean, it is difficult to see the difference if you change it slightly.
I think the appropriate main jet for the CBX1000 is between 105-140.
Currently, I change the main jet at around 128.
If it feels right, acceleration will increase significantly even at 1/2 to 3/4 throttle opening.
After that, I turn the throttle to full open and drive as fast as I can, but I still don't really know if the main jet is good or bad at full open.
It's hard to tell just by changing the slow jet one size at a time,
but if I change it by two sizes I can get a rough idea of ​​whether it's good or bad, but it always ends with a vague feeling rather than a "this is it!".
For safety reasons, the time you can drive at full open is only a very short number of seconds.
To select a main jet that you're truly satisfied with and are sure to find is one you'll need a chassis dynamometer.
Even without one, you can feel the main jet by feel.
Each time I change the main jet, I try full throttle, via 3/4 throttle.
A main jet that works well at around 3/4 throttle will also work well at full throttle.

I also check the condition of each gear position. I also pay a little attention to the revs.

I have heard from my predecessors that FCR tuning should be done without worrying about engine RPM.
I ride with the throttle open at about half in gears 4 and 5, checking the acceleration from 6000 RPM to full throttle. How does it rev up? How fast can it go?
If you can accelerate satisfactorily, then the main jet is appropriate.
It depends on how you rev ​​the engine and how you ride, but in the case of the CBX1000, you will quickly enter the red zone. When riding at over 150km/h, the oil temperature will quickly exceed 100 degrees.

A rev limit tuning of around 10,000 RPM is fine.

My CBX1000 is a CB1 model. When AS Wotani SP2 is installed, even if the rev limit is set to 9200 at dial [0], the CBX1000 cannot be driven at full throttle.
The rev limit can be increased comfortably even at 10,000 rpm.
In fact, it feels like the most comfortable acceleration is around 10,000 rpm.
I set the rev limit to 10,400 at [6].
The meters on old motorcycles are not accurate, but if you rev ​​it to the limit, it will misfire, so you may want to raise the rev limit a little more. In the case of 4th gear, the rev limit will reach the limit immediately.
In the case of 5th gear, adjust the throttle slightly while driving, and the speed will increase nicely.

Full throttle driving viewed in a complex manner

When deciding on the main jet, it is necessary to make a comprehensive evaluation as described above.
You have to ride while consulting with the rev limit.
On an old motorcycle like the CBX1000, you don't want to ride at the rev limit for long periods of time with the oil temperature exceeding 100 degrees. In the case of my CBX1000, I have removed the sensor from the oil pan. If you ride without paying attention, the temperature can rise to just under 110 degrees. Even though air-cooled engines are said to be resistant to temperature increases, it's not very pleasant, so I try to stop when necessary.

What air-fuel ratio are you looking at?

I try to keep it in the 12s range. I don't know if it's right, but
I feel like when I get to 13s, the air gets in and it slows down when I twist the throttle.
I try not to worry about the lean numbers showing for a moment.
My current feeling is that if I keep it in the 12s range overall, it will be tuned to give me a nice feeling of acceleration.

Meter Accuracy

So far, we have talked about the speedometer, tachometer, air-fuel ratio gauge, and oil temperature gauge. It is unclear whether the meters are exactly at 0, so you need to assume that there will be some degree of error.
They are not completely unreliable, but it is not a good idea to rely on them completely.
One thing I do rely on is the rev limit of the AS Wotani SP2. I don't know how accurate it is, but
at least at the moment of misfire, the engine speed is 10,600.

Rich or lean main jet size

In my opinion, changing the main jet from 125 to 130 changes the air-fuel ratio by about 0.5.
If you deviate too much from the optimum value, changing the jet will have no effect.

For FCR beginners – Set the rev limit a little closer to the limit

If you can operate the limiter, it's okay to leave it in the red zone a little.
However, you may not be able to feel safe.
Changing or disabling the limiter only while tuning is a safe method.
If the limiter is always left disabling, the engine may break if you let your guard down.
If you can test drive while paying attention to the RPMs and speed, it will be easier to test drive while tuning if you weaken the limiter a little.

FCR Tuning – Full throttle! Check the main jet for each gear【summary】

In summary, when driving at full throttle, tuning is required while looking at other factors as well as the throttle opening. At least in terms of speed, the power is being exerted to the limit, so nothing more. It is easy to understand what the state is like in the process leading up to that point. Once the throttle opening exceeds half, you can try various acceleration methods, such as changing gears at a certain number of RPMs, to see how the engine revs up.
In this article, we talked about selecting the main jet.
The cold season is still continuing, so please take care not to catch a cold.
See you again!

CBX1000 Photo Gallery

We will post a selection of photos from past posts, mainly of the side of the CBX1000.
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