FCR – Tuning with easy-access jets in mind

FCR – Tuning with easy-access jets in mind

Until recently, when I worked on the FCR of the CBX1000, I would try to change the jet as soon as I noticed something.
I set the FCR as a hobby. Time efficiency is a low priority.
The priority is to get results that I can be satisfied with.
Of course, there are times when I feel it is a hassle.
Now, let's get to the main topic.
I changed only the straight diameter of the jet needle by one step at low throttle opening.
The result was quite good.
As time passes, I forget about good results.
The FCR is a racing carburetor. Recently, I have come to think that it is better to frequently tune the parts that are easy to reach.
Of course, from the time I first started tuning, I tried to prioritize touching the jets and screws that are easy to access.
I'll tell you my story of failure: I once got some dirt in the slow jet, which caused it to run extremely badly. This was the result of repeating the same work in a day and losing my concentration.
Jets that are difficult to access should not be changed frequently.

Don’t change the slow jet casually

Before changing the slow jet, if you have a jet needle with a similar size, it is better to tune it or adjust it with the pilot screw or air screw. I've recently been thinking that you can change the slow jet when the adjustment range of the screw is not enough. There is a reason why I change the slow jet casually.
Because it's cheap. It's relatively easy to find the right size.
On the other hand, a jet needle costs about 700 yen.
For the CBX1000, you need six. That's 4200 yen.
Once you buy a jet needle, you want to touch a lot of them.
I never thought of keeping them in stock to change the size.
Jet needles are easy to access so you can change them casually.
When changing a slow jet, you have to drain the fuel, so it's not easy to access.
It can also damage the chamber packing.

The main jet is easy to access. But…

The main jet is not difficult to access, except for the need to drain the fuel.
However, since the fuel must be drained, it may not be covered by the title of this blog post. The main jet's range of effect is from about 1/2 throttle opening to fully open.
There are areas where its range of effect overlaps with the jet needle.
At full throttle, settings can only be made using the main jet.

Is the jet needle easily accessible?

In terms of work time, it may not be much different from the main jet.
In fact, there are more bolts to remove with the main jet.
However, you don't have to drain the fuel.
In that sense, I personally find the jet needle to be easier to change.
The main jet and jet needle do not affect the exact same range,
but changing the jet needle is very easy to notice while driving.

The most accessible is…

I would like to call it the idle stop screw, but my CBX1000 has a two-pronged throttle wire, so a vacuum gauge is basically required when touching the idle stop screw. There are two screws, one for 1,2,3 and the other for 4,5,6, so it is easy to access, but it is a hassle to adjust.

So for me, the easiest to access is the pilot screw.

The air screw can only be accessed by removing the Foam Air Filter Sock.

That said, it's not that much of a hassle...

The pilot screw is difficult to access due to its angle, but

it is easy to access if you have the tools.

It is often easy to see the changes when you touch it, but it is a bit sad that it does not have a big impact on tuning for driving.

I will write about the groups that are easy to access.

・Air screw
・Pilot screw
・Idle stop screw
・Acceleration pump adjustment plate

Easy to access means that it is easy to fine-tune.

For FCR beginners – Keep tools ready for the air screw and pilot screw

Touch the screw first rather than just changing the slow jet.
It is easy to access the screw.
The air screw depends on the characteristics of the vehicle, but it is sufficient to return all cylinders to the same position.
Try adjusting each cylinder separately if you can.
Depending on the type of motorcycle, it may be difficult to notice the change.
If you can see the change, adjust each cylinder separately.
If you cannot see the change, return each cylinder to the same position and adjust while test driving.
In many cases, you do not need to touch the pilot screw at all.
The engine's starting ability and idling will change in about 15 minutes.
You can make the same adjustment for each cylinder.
If you cannot notice any change when you touch the pilot screw, it is likely that the slow jet or straight diameter of the jet needle is extremely off.
If the slow jet is too rich, you can idle with the pilot screw all the way closed.
Easy access means easy touch.
Even if the engine is not running well, you can return it to its original state with little effort.

FCR – Tuning with easy-access jets in mind【summary】

To sum up, it's best to start by adjusting the areas that are easiest to tune. Slow jets are cheap and easy to get.
However, they take time to access.
If you have a lot of jet needles on hand, you probably won't change the slow jet frequently.
It's better to change the jet needle first, and if there's no improvement, then change the slow jet.
You can change the slow jet after you can no longer adjust it with the screw or jet needle.
Here's what happened in my case.
When I noticed that the throttle was opening at low speed, I would just change the slow jet.
If you want to completely change the feeling, it might be better to start by changing the slow jet.
For fine adjustments, changing the straight diameter of the jet needle is also effective.
This time, the advice was to start by adjusting the easy-to-access areas when tuning your FCR.
See you again!

CBX1000 Photo Gallery

We have selected some photos showing the jet needle and posted them below.