FCR Tuning – Throttle opening 1/16 determined by straight diameter and slow jet

FCR Tuning – Throttle opening 1/16 determined by straight diameter and slow jet

This is a story about using a jet needle that I bought a few years ago and hardly used.
The title says 1/16 throttle opening, but this is a story about low openings, including 1/8.
The other day, I looked back at my past logs about past changes in the straight diameter of SJ and JN.
My past and current experience levels are different, so the accuracy and precision of what I've written down will be different.
The number of slow jets and the straight diameter are quite related.
I'll write about that this time.
The initial tuning of my CBX1000 was a combination of
SJ slow jet - 42
Jet needle - 90FTM (clip stage unknown).
The first jet needle I bought was a 90FTN with a jet needle that changed the straight diameter from [M] to [N].
I didn't have multiple types of jet needles on hand, so I didn't know how big a change it would make by changing one number.
From there, I bought
90FTQ, 90FTR, 90FTS
in succession.
From there I changed the SJ in order and changed the clip stages a lot,
and now I'm just sort of tuning it to my liking.
I like FCRs because they give a sense of acceleration with rough throttle work.
The main topic is about the straight diameter and slow jet.
So let's get started!

The AS air screw and PS pilot screw are for adjustment purposes.

It seems a little strange to say that tuning is done with the AS air screw and PS pilot screw.
These screws are like fine adjustments for tuning at low throttle opening.
I currently think that they are there to balance out rich or lean at low throttle opening.
I think that anyone who touches them will probably end up with a similar return position.
The procedure is to use the slow jet and straight diameter to do rough tuning from idle to about 1/4 throttle, and then adjust the screws to get to the appropriate position.

If you change the straight diameter of the jet needle, also replace the slow jet.

Currently, I feel it is better not to change the straight diameter of the jet needle drastically.
Assuming that you can drive without stress to a certain extent.
Even if you change the straight diameter by one position, it seems that there is a certain amount of change.
If you want to see a change, change it by about two positions.
Even if you change only one place, the tuning situation will change in various ways other than the range of influence of the changed part. Now, to the main topic, the other day I changed the straight diameter of the jet needle by one position to be leaner.
JN-90FTM#1
SJ-48
→
90FTN#1
SJ-48

This change was extremely good.
I replaced the jet focusing on the area from idle to 1/8 throttle opening.
Even looking at the past logs,
JN-90FTS#2
SJ-52
was highly rated.
If you change the straight diameter from 2nd to 3rd lean, change the SJ to be 1st richer.
It's not a proportional matter like if you change the straight diameter by 4 places you should also change the SJ by 2 places.
I think the better method for tuning low throttle opening is to roughly decide on the SJ and then make fine adjustments with the straight diameter of the jet needle.
Changing the slow jet will make a big difference, and the straight diameter will make a medium difference.
I currently think that the other screws and clip stages will make a small or very small difference.
It sounds good if you can fine-tune the low throttle opening, but fine adjustments are essential.

Throttle opening 1/16 – Pilot screw is about to break

Idling is roughly adjusted with the SJ and pilot screw, with the main adjustment being engine starting. Since it is equipped with an air-fuel ratio meter, I try to keep it at around 12.5 to 13.
When the throttle is opened a little and the PS pilot screw's role is finished at around 1/16, the combination of the slow jet and straight diameter is important for tuning. I don't think adjusting the AS air screw has much of an effect. In actual driving, it is used during the starting process, and if you don't care too much about it, you don't need to use it, but I feel that when the combination of the slow jet and straight diameter is good, it connects very smoothly.

FCR for beginners – Buying jets

It is assumed that the motorcycle can be ridden without stress. The first thing I recommend you to buy is the jet needle to change the straight diameter by one size. Jet needles are the most expensive jets, so if you make a mistake in purchasing one even for a 4-cylinder, it will be sad.
It will be even sadder for a 6-cylinder.
You can slowly buy one size at a time and think about whether to buy in the lean direction or the rich direction. Since slow jets can be replaced with a combination of straight diameters or by replacing the slow jet alone, it is better to buy a set in advance rather than buying them little by little.
I have stocks from #35 to #52. And I still don't know which slow jet is appropriate. Recently, I feel that it is more efficient to change the straight diameter of the jet needle before replacing the slow jet.
When doing rough tuning, replace the slow jet. When fine tuning, such as when the tuning is already satisfactory, adjust the straight diameter.

FCR Tuning – Throttle opening 1/16 determined by straight diameter and slow jet【summary】

If the throttle is not working properly at 1/16 throttle opening, the combination of the straight diameter and the slow jet is not good. I feel like it is difficult to adjust with the air screw or pilot screw. I am not sure because I am not writing the results of a test. It is probably around the joint between the idle port and the slow port. It is a very small thing, so it is up to you whether you want to ride it without worrying about it. If you do not tune it often, you may not notice that it is not working properly.
My CBX1000 is equipped with an air-fuel ratio meter.
I felt that the air-fuel ratio was strange at around 1/16.
Winter is coming soon in Japan.
It is the season for motorcycle maintenance.
If you are not going to use it for a long time, please be sure to drain the gasoline and maintain the battery.
We hope you have a fun motorcycle DIY life.
See you again!