Comparison of FCR-jet needle cut-up. Let’s take a look at the thickness of the small standard 90FXM and 90FTM.

FCR-JN jet needle 90FXM FCR
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Comparison of FCR-jet needle cut-up. Let’s take a look at the thickness of the small standard 90FXM and 90FTM.

I recently received the JN Jet Needle 90FXM from BITO.

The previous blog post is related, so if you are interested in the details, please read it first.
tuning of FCR – If the small jet needle is F taper, you cannot choose the cut-up. Round up comparison

Now, I have JN with different taper and cut-up on hand.
I feel more and more like I'm buying it for experimenting rather than tuning it up.
What size jet needle do you really want?
I would like a cut-up count larger than 90FTQ, but since it is not available in standard stock,
I purchased 90FXM with JN installed in FCR of CBX custom-made by BITO.
I feel like this can be solved by changing the number of SJ and MJ and adjusting screws such as AS and PS,
It's a purchase.
Actually, the situation is that [F] taper jet needle does not have a choice of cutting up.
I'm so grateful. I tried to measure how many clip stages can be moved to the information based on the difference in rounding up.
Because 90FXM and 90FTM
[U] [V] [W] [X]
It should move upwards to 4th place.
The rounded length of 90FTM is [65.90]
The rounding length of 90FXM is [67.70]
It changes by 0.45mm at the 1st position.

Comparing 90FXM and 90FTM with calipers

Measure by adjusting the caliper to 2.6mm and inserting the jet needle from above.
We checked how much the number of clip stages changes.
This is the only way I can think of to measure it with a simple tool.
I tried measuring the tip of the JN to compare, but it seemed like it would damage the brass.
I didn't feel like I was going to be successful, so I gave up. Things that are angled in the 1/100 world
So I thought it was impossible. I have no choice but to trust the manual.
Left 90FXM, right 90FTM
The positions of the two-stage clips are generally different.
The pitch of the clip is 0.9mm, as measured by the manual and by our predecessors.
There is enough clearance for the clip to rotate.
I don't know how perfect precision is required, but I think that if you don't maintain precision at the first hit, you will be far from being able to set it with the precision that can be set due to disassembly and deterioration.

CBX’s next FCR tuning schedule

BITO factory tunings
PS-1.45 minutes back
AS-1.30 minutes back

My current CBX tunings are
AS-1.15 minutes
PS-1.30 minutes

What are your next plans?






I will try it like this.
As for SJ, the jet needle has become richer.
It looks like it can be adjusted with the AS and PS screws, so it seems like it can be handled around that.
There are no plans to make any changes.
I plan to do a test run and change the tuning order after seeing the results.

For FCR beginners – a little trick [warm up the engine]

Before changing the FCR tunings, it may be a good idea to warm it up before starting.
It is good if the engine startability improves a little. Just touch the carburetor with your hand.
There are two reasons.
① If you change the jet too much, the starting performance will be so bad that you will not be able to set it properly.
②Easy to attach and detach the carburetor.
Most assume the situation ①.
Although it depends on a case-by-case basis, it may affect the startability of the engine if something that is currently running deteriorates.
When things get bad, things can get out of hand.
You can avoid such situations. Also, if you discharge the accelerator pump pointlessly many times,
It can be assumed that the plug will get covered and there will be nothing that can be done about it.
Regarding startability, the only thing you can do is adjust AS and PS about once a day, keeping in mind the cold start.

Comparison of FCR-jet needle cut-up. Let’s take a look at the thickness of the small standard 90FXM and 90FTM.【summary】

The purpose of changing the jet needle is around 1/2 when the throttle is suddenly opened,
The purpose is to eliminate the symptoms of bumps or waiting to be opened.
If the problem cannot be resolved because the throttle is opened too quickly on purpose,
I think the only way to deal with it is by changing the way you ride.
With the jet needle I got this time, the number of clip stages is too low, but I am not sure if this is the cause.
I feel like I understand.
I won't know until I try it, so if it's sunny this weekend, I'll have fun tuning it up in the morning.
If that doesn't work, I'm considering trying the [G] taper tuning next.
I hope you all have a fun FCR life!
See you again!
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