FCR Tuning – Slow Jet Change – 22/10/24

FCR-Slow Jet Change FCR
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FCR Tuning – Slow Jet Change – 22/10/24

When I did a test run the other day, I was a little concerned about the low throttle opening.
The slow jet was set to 42 based on the time of BITO shipment.
This may be due to delaying the discharge timing of the accelerator pump.
It may be due to the season.
There is a part where the power is weak when starting from fully closed throttle opening.
For a moment, I was pointing to the air/fuel ratio as lean.
Changed slow jet from 42 to 48.
I changed the pilot screw because it was left open quite a bit.
Set it to rich considering that the accelerator pump will not be used when the throttle opening is low.
I think the appropriate slow jet for CBX is between 40 and 52.
Some have an acceleration pump, some have a straight diameter, and some have a number of clip stages.
The current CBX is not poorly tuned.
I will try to see what happens if I change it for my knowledge.
The theme of today's tuning is to avoid using the accelerator pump at low throttle openings.

There is also a history of making the slow jet richer from the current tuning in the past.
The related jets are slightly different.
Slow Jet 48 has a feeling of power and is my favorite tuning.
Change it to 48 again.
Slow jets should not be changed frequently.

FCR tuning – slow jet modification

I changed the SJ from 42 to 48.
I changed MJ from 125 to 130.
It is best not to change jets at the same time.
But I've changed.
The reason for this is that the range of influence is completely different, and the jets are changed while following past history.

[Current tuning]
AS-1.15 minutes
PS-1.30 minutes
Acceleration pump diaphragm KLX250
Acceleration pump discharge timing 1.6mm
AS Uotani SP2-Ignition [1]

I also synced it.
Unless the synchronization is extremely out of order, most of the time it ends with a confirmation.
It doesn't take long to work.

Things to check when taking a test drive

Up until now, I've been looking at the smoothness of starting and the ease with which the engine starts.
This time
① Is it smooth when starting from second gear?
② Doesn't it suddenly become lean around the border between idle port and slow port?
Please double check these two points.
Regarding ②, it is unclear whether there is really a boundary between an idle port and a slow port.
The air-fuel ratio meter shows lean at extremely low opening, so check to see if there is any change.
By changing the slow jet, I also tightened the pilot screw considerably.
The screw is set at a low opening so that it is easy to swing rich, so during the test run,
Decide on tuning by checking both by feeling and using an air-fuel ratio meter.
I was vague about the accelerator pump, so I'm looking forward to a test drive.

For FCR beginners – Throttle wire adjustment

Racing carburetors, including FCR, are forced open/close type carburetors.
Operate the throttle valve directly with the throttle wire.
This is the point that produces a sharp response.
You need to adjust the throttle margin and return strength to make it as easy to control as possible.
Excessive throttle margin or poor throttle return are not typical of a racing carburetor.
My throttle has no margin of 0mm.
It is close to 0mm.
Always check by turning the steering wheel left and right.
Regarding the throttle return, I try to return it too quickly so that it is too strong.
My CBX is equipped with a quick throttle.
The throttle can be fully opened quickly, with less margin, strict control, and the throttle closing speed is faster.
The strength of the throttle and the degree of opening to full throttle vary depending on your preference and purpose.
One of the best parts of racing carburetors is that they can perfectly reflect your preferences and uses.
Adjusting the throttle is easy if you try.
As a step towards becoming a beginner, please try tuning the throttle to your liking.
You'll be surprised how much fun you'll have when riding a motorcycle, even if it's not maintained properly.

work photos

My CBX has two FCRs in a set of three. There are two standard carburetors.
I am very curious whether the latest version of the 6-piece carburetor is easy or difficult to install and remove.

FCR Tuning – Slow Jet Change – 22/10/24【summary】

I find time to change the FCR jet.
Every time I attach or detach the cab, I find new discoveries or questions.
This time, I found a question, but it is unclear how to adjust the throttle tension regarding the return tension on the FCR side of the throttle wire. If you apply it too tightly, it will not move easily.
Since it has two crotches, it is difficult to match them exactly the same way.
I'm currently keeping it loose and thinking of it as insurance in case the throttle goes out.
It's not like I'm doing it randomly.
Today I decided to try it until I was satisfied.
But we didn't have enough time.
I will try it again the next time I install and remove the FCR carburetor to see what kind of effect it has.
I hope you all enjoy your motorcycle life.
See you again!
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