FCR Tuning – Slow Jet Selection – Start with the pilot screw back at about 1.0

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FCR Tuning – Slow Jet Selection – Start with the pilot screw back at about 1.0

I changed the slow jet regularly for 2 months. Changed to 40, 42, 48.
Returning the pilot screw allows stable starting and stable idling.
When checked with an air-fuel ratio meter, it returns to between 12.5 and 13.0.
I feel that if you return the pilot screw and air screw to a point above 2.0, there will be less change after that.
On the other hand, if you adjust the screw around 1.0, you will feel that the change is large.
The appropriate screw position changes depending on the slow jet size.
No matter what size slow jet you put in, just turn the pilot screw and air screw.
In the lower part, you can balance the balance.
Overlapping areas of influence between slow jet and air screw can be addressed by selecting a jet needle.
In the title of the blog, I wrote that I think it is better to set the pilot screw back to 1.0.
I'll explain what it means.
Determine FCR tuning from low throttle opening.
When the throttle opening exceeds 1/4 or reaches 3/8, it may become difficult to balance the balance.
There is no problem when idling even if the pilot screw and slow jet are opened wide at low throttle openings. Balance may be poor when the throttle opening is reduced to 1/4.
The range of adjustment can be very severe. .

This will affect the selection of the jet needle.

You should be careful when choosing a jet needle.
Even if the condition is good when the throttle opening is low, negative effects may appear as the throttle opening is increased.
The number of CBX's FCR jet needles at the time of shipment is 90FXM#3.
This is a jet needle with a special cutting edge.
It is not possible to choose the straight diameter.
If you reselect the taper, the entire tuning will be redone.
It is equivalent to using F taper and setting the number of clip stages to 1 from the top.
The straight diameter changes by about 6th, and the number of clip stages changes by about 1.
If you can choose as many straight diameters as you want, you can adjust the balance of tuning with a jet needle. For CBX, it is difficult to choose a jet needle.
The slow jet number can be tuned with the pilot screw returning 1.0 to 1.5 from the beginning.
It is better to choose it.
In the case of my CBX, I have started tuning with a jet needle around 90FTM or 90FTR. The number of clip stages should be between 1 and 3 when viewed from the top.
BITO also ships with a custom-made jet needle for clipping because there are not enough clip stages in the initial shipment. 90F series jet needles cannot be cut up.
If you wish to change the rounding up, you will need to place a special order.
If you want to change the cutting angle in a lean direction, you need to choose a 90G series jet needle.
BITO also used to ship jet needles at 90GTM.
*I inquired over the phone.

For FCR beginners – Be careful with chamber packing

Although extremely rare, gasoline may leak due to the chamber gasket.
When replacing the slow jet, it is necessary to remove and install the float chamber.
In rare cases, the chamber packing may break or become unusable.
When replacing the slow jet on the go, be sure to have a spare chamber packing.
It is better to refrain from replacing it. The only things you can touch on the go are the jet needle and screw.
It is also a good idea to have a spare clip for the jet needle.
Even if you don't have a jet needle clip, you may be able to get by by purchasing an E-clip at a hardware store. Chamber packing cannot be purchased normally.
Please be careful.

FCR Tuning – Slow Jet Selection – Start with the pilot screw back at about 1.0【summary】

If the pilot screw is around 1.0 and the engine runs smoothly, the air screw will also be around 1.0 to 2.0 in most cases.
You should be able to proceed with tuning in a well-balanced manner.
If in doubt, return the FCR to its factory tuning.
It is better to go back to the tuning that was good from the past history and try tuning again.
Bad changes in tuning are usually caused by something changed before or after.
That includes things other than tuning.
In the case of my CBX, I became more serious about tuning after installing quick throttle.
There are only a few days left in 2022, but please enjoy a fulfilling FCR life.
See you again!

*Recently taken CBX photos are posted below.

CBX-Photo Gallery

The CBX photo and tuning manual that were taken close to the date of the photo state that the pilot screw should be started at 1.0. For the air screw, change it by 5 minutes in each cylinder,
A good way to do this is to decide when the rotational speed has increased, and then increase the richness for about 5 to 10 minutes. In the case of CBX, it is difficult to discern the differences between each cylinder. After that, adjust the pilot screw to the return position for good starting performance and you will be able to drive comfortably.
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