Notes on changing FCR slow jet

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Notes on changing FCR slow jet

I'm not good at replacing the FCR's slow jet.
I don't like it, or rather, I've started to dislike it lately.
The reason for this is that slow jets are often involved when troubles occur.
This time, I will be posting a blog focusing on the troubles when replacing slow jets.
This is not a particularly maniacal story or a story about CBX1000, but a very common story.
Let's start!

Changing the slow jet takes a lot of effort.

CBX1000 has 6 caburetors.
The jet change is 6 times that of the SR and 1.5 times compared to a 4-cylinder motorcycle.
It's a pain. Purchasing a new jet also costs 6 times more than an SR.
I don't regret it too much since I'm using the money for my hobby.
However, it is better to spend less money.
In addition, FCR's slow jet is not easily accessible.
I will briefly write down the work procedure for CBX1000.
①Remove the tank
②Remove the right throttle wire (because it is a two-branch cable)
③ Remove the left throttle wire (because it is a 2-branch cable)
④Remove the cab
⑤Remove the FCR float chamber
⑥Slow jet change
⑦Install the FCR float chamber, being careful of the gasket.
⑧Attach the caburetor to the motorcycle
⑨ Attach the throttle wire while adjusting the left and right when the throttle is fully open.
⑩ Roughly adjust the screw to start the engine
⑪ Perform synchronization work

It takes quite a process. I don't want to do it all the time.
I do it all the time.
If it's just a hassle, just take the time.
CBX1000 has 6 cylinders.
The trouble occurrence rate is also 6 times higher than that of SR.
With this in mind, I would like to introduce the trouble that occurred when I changed the slow jet.
Knowing the troubles that are likely to occur even on non-CBX1000 motorcycles will be useful for troubleshooting on other motorcycles as well.

Attaching and detaching the plug cord

There are rare cases where the plug cord comes off when installing the tank.
If the engine is not lit, the temperature of the exhaust pipe will drop and the exhaust gas will smell like gasoline.
You can clearly hear it even by sound.

clogged slow jet

Before installing the slow jet, make sure that there is no dirt mixed in on the receiving side. You can also blow it away with parts cleaner.
Also check that the slow jet hole is not blocked.
Just checking to see if light is passing through will reduce the chance of trouble occurring.
This is an item that is difficult to notice when working in multiple ways.
If you feel that the engine is not revving properly or that something is wrong, try taking measures such as returning to the jet before the change. If the symptoms improve, either there is dirt attached to the slow jet or the slow jet is defective. It can occur in the main jet as well as in the slow jet. please note.

Gasoline leaks from chamber gasket

If the chamber gasket is misaligned or too thin, gasoline will leak.
Once the fuel has descended into the chamber, check for gasoline leaks.
If you do not notice this while driving, it may cause a fire.


This is a phenomenon where dirt gets stuck in the float valve, causing gasoline to leak from the air vent.
When gasoline gets into the engine, it dilutes the oil and can be very dangerous.
Otherwise, the connecting rod may be bent.
The solution is to turn the fuel cock on and off properly and smell the oil to make sure it doesn't smell like gasoline.
The probability of this problem occurring when changing the slow jet also increases.

Caught on wires

If the throttle wire and clutch wire do not return properly or when you turn the steering wheel,
There are also cases where there is a catch. This can happen when the gas tank is installed or removed rather than when changing the carburetor. Please check the clutch and throttle handling after turning the steering wheel.

Bolt falling off

I forgot to tighten the bolt.
There are many cases where it is temporarily fixed and you only notice it after some time has passed.
It's hard to notice things like main jets and slow jets falling off after some time has passed.
Also, if the jet needle fixing bolt falls off, the throttle will not return, which is dangerous. This is a problem that can occur the more bolts are tightened. Get into the habit of checking things without rushing. This is a common problem.

Jet screwdriver

This is a problem where the jets are tightened too tightly and the threaded parts are torn off.
The tuning parts are made of brass. Since it is a soft material, it will easily break if you tighten it too hard.
Please be careful. If you are concerned, you may want to try cutting off the threads on purpose using an unnecessary main jet to test the amount of force. I feel an unpleasant sensation in my hand the moment it breaks.

Bolt trouble

Even if the screw gets licked, it can be handled in most cases.
Here I will write about an example that is not very good.
Please refrain from using stainless steel bolts. If the thread is cut, we may not be able to fix it, or it may take more time to fix it.
Although it may be used in some places, unexpected problems may occur if iron and stainless steel come into contact or if stainless steel is used around electricity.
Manufacturers should not use stainless steel bolts at the time of shipment.
Stainless steel bolts can be a nuisance. Please understand the intended use before using it.

For FCR beginners – Checking the tightening of bolts

The above is everything, but I will write down the main points.
There is a high possibility that the above problems will occur if you are concerned about the speed of your work or if you are a beginner. This is due to worrying about the work speed, or neglecting to check it because you have gotten used to it.
There are some problems that you won't encounter unless you get used to the work.
The more problems you encounter and the more you solve, the more your skills improve.
The same goes for non-motorcycles. Although it is better not to encounter them, there are many problems that can be avoided just by reading the text in advance. Be careful when you get used to the work.
A motorcycle will not be damaged by FCR tuning.
You can tell that something is wrong before it breaks.
Changing slow jets is risky.
You can't rely on it if it becomes inoperable while you're out and about. I was changing the slow jet on the go.
After reflection, I decided not to change the slow jet or attach or detach the carburetor on the go.
Please keep this in mind.

Notes on changing FCR slow jet【summary】

I'm probably not as good as a professional, but I do a lot of FCR tuning.
I have also encountered some troubles.
I wrote this down from memory.
Writing down what I learned in writing allows me to reconfirm myself, so it is very helpful for me.
I may have written this several times, but the above is a problem that can actually occur. Everyone please take note.
Please enjoy your FCR life.
See you again!

*Photo gallery is posted at the bottom.

Photos of CBX1000’s FCR work system

I will post photos of disassembled motorcycles and skeletonized motorcycles.
SEP bearing guide and 90FXM jet needle are my favorite items these days.
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