FCR Tuning – The pilot screw can be fully closed to allow idling.

HONDA CBX1000-cowl FCR
This article can be read in about 13 minutes.

FCR Tuning – The pilot screw can be fully closed to allow idling.

Recently I have been posting about tuning FCR at low throttle openings.
This time it's about adjusting the pilot screw.
There is a lot of writing depending on the situation.
Different people will say different things.
What is written also varies depending on the source of the information, such as magazines or online articles.

『Nowhere does the engine react as severely as the PS.』
『1.0 RPM is fine.』
『PS is not very effective, so there's no need to touch it.』

I've heard and read a variety of opinions.
They're all probably correct. The way of thinking differs depending on the tuning precision you want.
These opinions come up because
the range of influence of the PS is narrow and it's difficult to access the Parrot Screw.
The above are opinions that do not overlap.
Post title
『Idling even when fully closed』
At first, I also didn't really understand the cause.
In my opinion, idling shouldn't be possible.
Reading the tuning manual carefully didn't solve the problem.
The solution to my pilot screw problem was the Pilot Screw Adjusting Tool.
I couldn't find a Pilot Screw Adjusting Tool that would allow me to adjust the CBX1000 while it was idling, so I modified the Pilot Screw Adjusting Tool I had to make it compatible with the CBX1000. At the introductory stage, there are four topics,
but I will explain them one by one. If you have any questions about the pilot screw, this may be helpful.
So, let's get started!

The pilot screw will idle even when fully closed

To begin with, CRS carburetors do not have a pilot screw.
They do not have an idle port either.
They idle using fuel supplied from the slow port and air from the gap in the floating valve.
If the slow jet is made extremely large, it will cause symptoms as if the pilot screw is not working. When it gets to that state, you can close the pilot screw all the way and the engine will idle normally.
It doesn't feel like something is wrong. You can ride the motorcycle normally.
This means that you can also turn off the pilot screw function.
Of course, this is not a very pleasant experience, so I try to leave the pilot screw open about one turn.
By the way, if I closed the air screw all the way or did something extreme, the engine of my CBX1000 would stall.

『Nowhere does the engine react as severely as the PS.』

The range of influence of the pilot screw is quite narrow.
When the correct size slow jet is introduced, we can see that it is a screw that fine-tunes the fuel supply around the throttle being fully closed. All cylinders have the same return, but the change can also be seen with the air-fuel ratio gauge.
When viewed with a digital tachometer, the change in RPM is not very clear.
If the pre-tuning is within the correct adjustment range with the correct slow jet,
it is functioning well enough that you can see the change.
Without the Pilot Screw Adjusting Tool, you will need to remove and attach the carburetor every time to make adjustments,
so the change may be difficult to see.
It is difficult to see the adjustments made to make it rich,
but it is easy to see the adjustments made to make it lean.

『1.0 rotation is fine』

This is a phrase you often hear.
In short, there is no need to touch the PS because the tuning manual states that the proper setting is one turn back.
It means that if something is wrong, change the slow jet.
This may have originated from the CRS carburetor, the predecessor of the FCR.
If you don't adjust the PS, you have no choice but to adjust the slow jet instead.
Every time you remove the carburetor, drain the gasoline, remove the chamber, change the slow jet,
adjust the throttle, etc.
It's a lot of work. When I didn't know how the pilot screw worked, I did almost all of the above.
At least, there's nothing wrong with it from the perspective of the tuning results.
Rather, it's a way of thinking that doesn't accept anything other than a well-balanced and proper slow jet.
There's a difference between blindly fixing the pilot screw adjustment without knowing it and fixing it knowingly.
In either case, if the engine is hard to start, opening the pilot screw about 15 minutes at a time using the hands of a clock will stabilize the idling.
If you know the theory, this is a possible tuning method even without a Pilot Screw Adjusting Tool.

『PS is ineffective, so there’s no need to touch it.』

It's a combination of the above.
There are many factors, such as setting the idle a little higher, using a rich and large slow jet,
or the slow jet and pilot screw having already been properly pre-tuned. If it's running well, there's no need to touch it...it's the opposite way of thinking.
If the idle is not running badly, there's no need to touch it...
No matter how hard you try to improve the idle, your motorcycle's horsepower will not increase.
It would be strange to tune in search of the ultimate idle.
In any case, if there's no change when you adjust the pilot screw,
there is a possibility that the tuning is unbalanced in some way.

For FCR beginners – In many cases there is no problem with the air-fuel ratio being in the rich direction.

It's not good to overdo things, but there are almost no problems with tuning rich. In fact, leaner tuning will cause problems.
The correct air-fuel ratio and tuning is to find the air-fuel ratio that is just before it doesn't cause problems. If you change the jet needle clip stage to rich, the engine will not rev up. However, it won't break. I feel that it tends to be difficult to tell when the air-fuel ratio is adjusted to the rich side, as it is less likely to cause problems. Basically, if you try to change the air-fuel ratio from rich to lean, it is easy to find the best tuning. Tuning is a repeated AB test, so try to get a feel for rich or lean in your own way.
If the engine is not running well because it is too rich, it may be because the accelerator pump is too strong, so it is difficult to generalize. If the engine is not running well even though the jet is lean, it may be because of the accelerator pump. If you turn off the accelerator pump and then change the jet from rich to lean,
you will be able to find a good tuning without getting lost.
It will take time to change the jet and test run it, but at least it won't go bad and you'll end up in a quagmire.

FCR Tuning – The pilot screw can be fully closed to allow idling.【summary】

I had gotten used to it, so I had forgotten about it.
When I first started tuning the CBX1000's FCR, I didn't really understand what the pilot screw was.
I work with computers, so I often search the internet,
but it seems like there are a lot of vague articles about pilot screws.
And so here I am, posting a blog online,
but maybe I'm one of those people who don't understand much about pilot screws.
At the very least, I've written this based on the results of my own experiments.
Please take this as one opinion of someone who is tuning the FCR on a CBX1000 motorcycle.
I'm sure you're all busy tuning your FCRs too.
Let's enjoy tuning the FCR together.
See you again!

CBX1000 Photo Gallery

Here is a photo from a previous blog post that shows a neat and tidy CBX400F Integra cowling attached to a CBX1000.
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