FCR tuning-Change Accelerator Pump diaphragm and test run

This article can be read in about 9 minutes.

FCR tuning-Change Accelerator Pump diaphragm and test run

Today, I did a test run for about an hour during lunch time.
The aim is to change the diaphragm of the Accelerator Pump from standard size to small size,
I wonder if the bumpiness that occurs when the throttle opens suddenly around 1/2 will be resolved.
As a result, I feel like there has been some change, but it's unclear.
After that, try widening the link lever plate and slowing down the accelerator pump as much as possible to see how the accelerator pump starts to work.
I felt that the feeling of bumps had faded to some extent, but it was not completely gone.
The bumpy feeling didn't go away that much, but when I did a test drive, I found it felt great when I turned down the acceleration pump. I don't like how the bumps remain when the throttle is suddenly opened.

Things I want to try on my next setup

Because the MJ main jet was made extremely large,

Let's lower the count and see the change.
Since the SJ is also large, it seems okay to lower the count.
I lowered the temperature by one degree and did not see any improvement in symptoms.
Regarding JN, no change was observed even when the straight diameter was made leaner.
I'm going to lower the MJ number and do another test run.
If there is no change, lower the SJ to the extreme and check again for bumps during sudden opening.

Accelerator Pumpのlink leverを4.8mm以上にする

It is written in the manual that the timing of the Accelerator Pump is adjusted, but even if it is set above the specified value,
It seems to be discharged at around 3/4 to 7/8 throttle opening.
I understand that the link lever can only adjust the throttle opening up to 3/4.
It no longer reliably ejects when the throttle opening is 1/2.
This time I would like to explore the bumps around 1/2 throttle opening, so here are some details.
I try not to worry about it too much.
I did a rough test during a test run, so I didn't measure it with a signage gauge, etc.
It is definitely widened by more than 5mm.

Things I noticed while writing this blog after taking a test drive

I didn't notice it during the test drive, but when I thought about it more carefully while writing this blog, I realized that
The air-fuel ratio meter may read 10.0 when you open the throttle suddenly.
I think this is due to the Accelerator Pump being too effective.
If you think of it that way as a hypothetical, there are many things that don't make sense.
As a test, instead of changing the timing of Accelerator Pump, try tuning it off completely.
If the air-fuel ratio meter does not show 10.0 when you suddenly open the throttle with the accelerator pump not working at all,
This proves that the Accelerator Pump is too effective when the throttle is suddenly opened.
You will also be able to set the Accelerator Pump based on the air-fuel ratio meter.
You will be able to visually control the discharge timing and total discharge amount of the Accelerator Pump.
In fact, I'm very happy because it's an item that can't be controlled just by feeling.
I was a little concerned about the effectiveness of the Accelerator Pump after tuning the throttle high.
The winding of the throttle wire is nearly twice as large as before, so the speed at which the throttle can be opened quickly is also nearly twice as fast. This means that the amount of movement required to push the Accelerator Pump's push rod has also doubled.
If you think about it calmly, it's normal for it to get richer.
This assumption is probably correct, so I'm looking forward to verifying it.

FCR tuning-Change Accelerator Pump diaphragm and test run【summary】

This time, I was able to gather some hints about the tunings of the Accelerator Pump.
The point is that the discharge timing and total discharge amount of the Accelerator Pump may be determined by the maximum value of the link lever adjustment and the air-fuel ratio meter.
The fact that there is no change in the main jet may mean that it is beyond the range where you can feel the change. This may be a misplaced range.
Or maybe you're looking at the wrong throttle opening in your judgment.
Looking at the influence range part of the FCR manual, when you want to change 1/2 in the taper explanation
It says that it should be replaced in combination with the MJ main jet, so
On the other hand, the air-fuel ratio around 1/2 throttle opening seems to be affected by MJ.
I think I should change MJ and see how much of a difference there is.
I'd be happy if this changes what I had assumed, so next time I'll lower the MJ count to a leaner one and do a test run.
I hope you all have a fun FCR life.
See you again!

*Work photos are added below.

work photos

It's rough, but I'll attach a photo. It's better than not having a throttle opening marker.
There is play in the throttle, and the tension of the throttle wire changes every time you install or remove the carburetor, so the position changes slightly each time.
Copied title and URL