FCR Tuning – Changed SJ from 38 to 40. PS pilot screw adjustment-22/09/28

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FCR Tuning – Changed SJ from 38 to 40. PS pilot screw adjustment-22/09/28

Changed SJ from 42 to 38. Before the change, there was no need to worry about tuning. However, although the AS air screw was within the allowable range, I felt that it was being returned too much.
Changed to 38. I haven't tried SJ38 since changing to the current JN jet needle.
This is a change in search of something new to discover.
As a result, the engine started poorly this time, and the PS pilot screw was returned too far.
There was a process like that, and I changed to SJ40. The factory tuning for BITO is also SJ40.
The seasons are changing, and I don't want to change my SJ throughout the year, so I went with the safe SJ40 this time.
SJ believes that in addition to the range of influence of the screw, it also affects the throttle opening from fully closed to 1/2.
I would like to make a major change to SJ.
The situation is such that the current JN cannot choose a straight diameter.
For the time being, the choice is between SJ40 and 42.

Adjusting the screw when starting a cold engine

Until last year or so, before installing or removing the carburetor, I would warm up the engine to about 50 degrees with the sound of oil before installing or removing the carburetor. The reason is that engine startability becomes poor when the carburetor is installed or removed and the tuning is drastically changed. Especially when it's cold and the engine doesn't start in the winter, the plug may get covered, which is the worst.
Recently, I finally noticed the screw tuning.
I don't know if it's the right way to do it, but in my opinion the engine starts easily even when it's cold.
Idling is also easy to maintain.
Check the throttle opening between fully closed and 1/8.
I am in charge of idle ports and slow ports.
① Set the AS to a slightly richer position. If you are unsure, just set it back 45 minutes.
② Set the PS back by 1.00 minutes. Send fuel several times with the accelerator pump, wait about 10 seconds or more, then turn the cell. The engine starts, but it gradually loses its power and I can't keep it idling with the engine fully closed.
③ Open the PS for about 15 minutes at a time. Gradually, the time you can maintain idling when fully closed becomes longer. If the engine is about to stall, open the throttle to about 1/8 to let the mixture breathe.
Open the throttle quickly while moving it in small increments.
④ Open the PS to a point where it is easy to maintain idling and it is finished.
This is temporary, so when adjusting AS during a test drive, open and close PS to adjust.
In the case of CBX, I have never had a situation where I opened the PS too much and it became too rich and caused problems with driving, but I start with the PS from a lean state to a rich state.
It is clearly written in the tuning manual that you should perform temporary tuning starting from PS1.00 and proceed.
It might be a good idea to turn the PS back by 3.00 minutes and then tighten it until the idling becomes unstable, but I've never heard of a clear reason why.
I have three reasons.
① The engine will not seize at low openings.
②If possible, it is desirable to set the PS back by 1.00 minutes.
③ When idling, fuel is consumed more than expected.
For that reason, I start with a low PS of about 1.00 minutes.
Lately, I've been using the above method to start the engine when it's cold, and it stabilizes the engine fairly easily. Please be careful as the AS will not be in the correct position just because the engine starts.
Replacing the SJ takes time, so we recommend doing it in moderation. Other jets are easy to maintain, as Keihin's designers don't ask us to change them frequently. It is better to adjust the screws frequently, and it is also a good idea to change the number of clip stages on the JN as soon as you notice it. It's not that you don't need to touch the SJ often, but it's structurally difficult to touch, so the screw works on idling and low opening.

For FCR beginners – It may be a lie that you don’t need to touch the PS pilot screw.

There are many factors such as the type of motorcycle, season, and temperature.
There are some tuners who are told or are told that the pilot screw does not need to be touched from 1.0 onwards. If the engine starts easily and there are no problems, 1.0 is fine.
1.0 is fine in most cases.
However, if you find that the engine is having trouble starting or idling for a long time,
Try opening the PS pilot screw in 15 minute increments.
This section is written for beginners, so I don't recommend playing around with the PS too much.
There may be an improvement in engine startability.
By the way, unlike AS, it is difficult to notice changes in PS.
The fact that the changes are difficult to understand may also be the reason why it is said that there is no need to touch the PS.
Some motorcycles allow you to warm up the motorcycle by opening the throttle slightly without having to fully close the throttle.
Such motorcycles may not need to worry so much about PS. All you have to do is open the throttle a little and wait until the engine warms up.
In short, not everything needs to be changed from the initial values such as PS1.0.

For FCR beginners – How much does the adjustment range of the screw change when replacing the slow jet?

Although it is not recommended for beginners, if you change the SJ slow jet first,
How much does it affect the screw?
This is the case when looking at the influence range in the tuning manual.
Overall fuel consumption will increase by about 15%.
Whether it's the air screw or the pilot screw, the effect is about half a turn.
Strictly speaking, not all areas of influence overlap, so there are complex changes.
If you make SJ the richest, AS will open a little more than half a turn and be about the same as before the change. PS is about the same level by tightening it a little more than half a turn.
It means that.
The reason why the influence ranges do not overlap exactly is that it would have been better if there had been a slight change when changing the count.
I think this is because there is no throttle opening that makes tuning impossible.
Although it is not absolute, it will be helpful when purchasing an SJ to remember that changing the SJ will affect the screw by about half a turn.

FCR Tuning – Changed SJ from 38 to 40. PS pilot screw adjustment-22/09/2【summary】

It's a bit troublesome to remove the appropriate range for SJ.
This is because SJ requires a lot of time to replace.
I think that the design philosophy of FCR development is to use JN's straight diameter.
We search by hand for motorcycles for which we do not have data or for which an air-fuel ratio meter cannot be used. It will take quite some time.
If you don't have an air-fuel ratio meter, even if the SJ and jets are correct, it is difficult to judge whether the jet is the correct jet or not unless you swing it to the wrong side and feel no change.
It is important to think logically, but after thinking about it, try exchanging it anyway.
Try it out and see if you like it.
I haven't replaced SJ continuously recently.
I noticed a lot of things, so I'll write another blog post.
I'm sure everyone is busy tuning their FCR.
Thank you for reading to the end.
See you again!
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