FCR Tuning – Will tuning improve the return to idle?

FCR Tuning – Will tuning improve the return to idle?

There is something I pay attention to when tuning the FCR of the CBX1000.
Synchronization means adjusting it frequently.
This time, I will write about the FCR Return to idle when idling, including synchronization.
I may have some assumptions or misunderstandings.
However, some of the items may be correct.
Some vehicles have engine characteristics that make the RPM drop easily. You can tell by comparing the engine sounds of a sports car and a truck. There is also the characteristic of the flywheel inside the engine.
Regardless of the quality of the tuning, the RPM will return quickly.
A faster Return to idle makes it feel more racy and cool.
When I synchronize, I am concerned about the Return to idle, so I make sure to rev it up beforehand.
The state changes every time I touch the FCR, sometimes it returns quickly and sometimes it doesn't.
This is not about the Return to idle being slow because the insulator is sucking in secondary air or because of vehicle maintenance, but about whether the Return to idle can be made faster by tuning.
First of all, it's not that tuning changes Return to idle.
It's also possible that poor tuning is the reason Return to idle is slow.
I'll write about the results of various attempts I've made.

Reasons for slow FCR return to idle on the maintenance side

Here are some of the most common issues.
1. Secondary air is being sucked in through the insulator.
2. The body is worn and the throttle valve is not returning well.
These two are roughly the physical causes.
In terms of motorcycle maintenance, there may be other causes.
I think the reasons for slow return to idle due to lack of maintenance can be broadly divided into the above two points.
It could also be caused by the throttle wire getting caught.
In general, return to idle seems to be slow when symptoms of a lean air-fuel ratio appear.

Return to idle will not be fast unless synchronization is completed.

I often synchronize my carburetors.
This is for multi-cylinder engines.
When the engine is cold, the RPM is pulled by the lower carburetor.
When the engine is hot, the RPM is pulled by the higher carburetor.
If you care about return to idle, synchronization may be one thing you need to worry about.

Reduce idle

Lowering the idle slightly will make the return to idle faster.
It may not be that a lower idle speed makes the return to idle faster, but rather that the range of influence of the jet changes slightly. Lowering the idle speed may make the effect easier to understand.

How are you tuning?

Fully closed,
throttle opening 1/16,
throttle opening 1/8,
throttle opening 1/4,
I try to keep the ratio around 13.
I adjust the discharge timing of the accelerator pump so that it works at throttle opening 1/2 or more.
I tried the slow jet number from small to large.
I try to keep the air-fuel ratio around 13.
There was no particular change.

What about ignition timing?

My CBX1000 is equipped with AS Wotani SP2.
I feel that the return to idle is faster if the ignition timing dial is advanced.

This is a reference video.

You should see Return to idle, Sync and A/F. Sync is mostly correct.
I'm working on calibrating the vacuum gauge.

For FCR beginners – There’s no harm in checking the throttle area

You don't need to be an expert on motorcycles to do this. You can adjust the idle with the idle stop screw. However, the synchronization may be slightly off.
Is the throttle valve fully open when the throttle is fully open?
Is the throttle wire stiff when you turn the handlebars left or right?
Just checking these points will reduce the risk of accidents while riding.
This is an easy job.
The FCR is a forced opening and closing carburetor. It is a carburetor that allows you to enjoy the quick response of throttle operation.
It is important to check the throttle condition regularly.

FCR Tuning – Will tuning improve the return to idle?【summary】

If the return to idle is slow, it is likely that the tuning or synchronization is off.
There may be multiple contributing factors, such as the throttle wire or idle stop screw.
It may be caused by deterioration, such as a cracked insulator.
I am trying out what you have written.
My CBX1000 doesn't have any issues with return to idle.
There should be one of them that is correct. Or if you try them all, your motorcycle should be in good condition.
I don't enjoy tuning the FCR just by worrying about the engine's return to idle.

I will write another article next time after I have tinkered with the FCR in various ways.
See you again!

CBX1000 Photo Gallery

We will select photos from the past logs, mainly photos taken during synchronization work.