FCR Tuning – Easily Adjusting for Each Season

FCR Tuning – Easily Adjusting for Each Season

There are various owners when it comes to FCR tuning, ranging from those who want it to be perfect to those who are satisfied with about 80% accuracy. Ideally, I would like to maintain a perfectly tuned state all the time. However, there are challenges such as technical difficulty and the lack of necessary tools or jets.

In this blog post, I will discuss how to easily adjust FCR tuning for each season. Setting it slightly rich is usually sufficient for trouble-free riding in most cases. As long as the engine starts and idles, you can ride, although the overall condition may be unclear.

Once you establish the FCR tuning for spring and autumn, you can make simple fine-tuning adjustments to ensure year-round riding. The tuning for summer and winter may not be perfect, but it will be less stressful.

This assumes that the FCR is ideally tuned for spring or autumn. I will provide specific adjustments for summer and winter. So, let’s get started!

Difficulty Level 1 – Idle Stop Screw

If the idle or engine starting is poor, adjust the idle stop screw to set the idle speed. Adjusting the throttle slightly won't make a difference. Although I've labeled this as Difficulty Level 1, if you're using a dual-throttle cable type like on the CBX1000, there might be two idle stop screws, so be careful. You might need to resynchronize the carburetors.

Strictly speaking, even if you're using a single-throttle cable type, it's still advisable to synchronize the carburetors. This is because the vacuum levels can vary across cylinders, so it's not guaranteed that all cylinders will have an average vacuum level.

Difficulty Level 2 – Using the Accelerator Pump as a Choke

Before starting the engine with an FCR, twist the throttle about three times to squirt fuel from the accelerator pump and wait about 10 seconds for the fuel to vaporize before starting the engine. I’ve labeled this as Difficulty Level 2 because you need to get a feel for it. Overdoing this can lead to fouled plugs, which is not ideal. In winter, it’s also important to wait a bit longer for the fuel to vaporize. Although this is more about starting performance in winter rather than tuning, getting the engine started is essential before you can perform any tuning.

Tuning should be done after the engine temperature has risen. Tuning is not recommended when the temperature is below 5°C (41°F). Making the engine easier to start through tuning is a very important step.

Difficulty Level 3 – Pilot Screw

The difficulty of adjusting the pilot screw can vary significantly depending on the motorcycle. Simply put, the key point is whether you can accurately adjust the pilot screw while the engine is running. In some motorcycles, you might need to install the FCR in a configuration where you cannot access the pilot screw. For example, the CBX1000 has a carburetor configuration where the Carburetor Pilot Screw Adjustment Tool is very difficult to use. I have custom-modified a Carburetor Pilot Screw Adjustment Tool specifically for the CBX1000. Adjustments are made by opening or closing the screw depending on the season. The aim is to improve engine starting and idling. Ideally, you would like to adjust it, but in winter, you might turn it rich for about 15 minutes. In summer, adjustments such as closing it for 5 to 10 minutes might be sufficient.

Difficulty Level 4 – Air Screw

This affects the throttle opening from 1/8 to about 1/2. The strength of the impact varies, but it influences the idle and mid-range used in city riding. In winter, adjust slightly richer by turning it in for about 15 minutes. In summer, adjust slightly leaner by turning it out for about 15 minutes. This screw is relatively easy to feel, so it is beneficial to experiment until you are satisfied.

Although removing and attaching velocity stacks and air filters is necessary, accessibility is generally very good.

A key point is to clearly remember the initial position of the screw and take notes regularly while making adjustments. Depending on the motorcycle, some shops adjust the screw differently for each cylinder. For my CBX1000, even setting the same screw position for all cylinders does not show perceptible differences. Adjusting to the same setting is generally fine for 80% accuracy. The key is to check if there is a solid power feel when engaging the clutch and starting to ride. Adjust in increments of about 5 minutes until you reach a satisfactory setting. The motorcycle's performance should improve significantly

Difficulty Level 5 – Jet Needle Clip Positions

The way the motorcycle performs will change drastically. When tuning roughly, it is more about finding a setting that matches your own feeling rather than strictly chasing the air-fuel ratio. As a result, whether it is too lean or too rich, the best setting is the one that feels right to you.

At this point, the difficulty increases, as it may involve removing or disassembling the carburetor. Once you start adjusting aspects like the straight diameter or taper angle, it moves beyond the goal of simple tuning. Up until this stage, the tools required are minimal for easy tuning.

You should not experience issues that cannot be reverted if the tuning becomes problematic.

Difficulty Level 6 – Changing the Main Jet

The difficulty level increases slightly. This is an item where changes are easy to notice. Change the main jet size by about two sizes at a time.

You can feel the change in acceleration when you open the throttle aggressively past about 1/2 throttle. If you can't detect the change, it's likely that you are significantly outside the proper jet size range.

It is particularly hard to notice when you are significantly lean. Changes are more apparent when you are rich. Even if judging the change is difficult, adjusting two sizes richer in winter is a good approach.

Slow Jet and Others, etc.

Tuning aspects of the FCR not mentioned above are not simple. The timing of the accelerator pump discharge can be adjusted relatively easily. However, adjustments regarding the total discharge volume and seasonal variations may not be straightforward. Changing the slow jet is quite labor-intensive and is not a jet that is frequently changed. Sometimes, adjustments involving the straight diameter may be required. Once you determine the appropriate combination of the slow jet and the jet needle’s straight diameter, it is better not to make frequent changes. Depending on the tuning aspects, changes may be hard to notice or result in complex effects.

For FCR Beginners – Asking a Motorcycle Shop for Tuning

Up to difficulty level 6, it is easier to manage if you ask a motorcycle shop for thorough tuning and then handle minor adjustments yourself, working together as a team. Repeatedly removing and reinstalling screws, the carburetor, or the throttle cable can cause the carburetor synchronization to drift slightly over time. To maintain optimal performance, it's advisable to have the carburetor synchronization checked once a year or have a comprehensive tune-up every two years.

From the perspective of the motorcycle shop, servicing a motorcycle they have previously worked on is easier, so they will provide high-quality work.

For FCR Beginners: Start by Adjusting What You Can

It's important to start by trying things out. If you're referring to this blog post, the tool you'd want to have is the Carburetor Pilot Screw Adjustment Tool. This falls into the category of special tools. Depending on the motorcycle, there may be models that are not compatible. If you know someone nearby who has the tool, you might want to ask if you can test it.

If that's still difficult, you might need to repeatedly buy and sell different Carburetor Pilot Screw Adjustment Tools on auctions until you find one that works for your motorcycle.

FCR Tuning – Easily Adjusting for Each Season【summary】

Aside from the extreme temperatures of mid-summer and mid-winter, most of the adjustments can be handled within the scope described above.

The level of tuning, the time spent on tuning, and the number of tuning jets you have are all factors to consider. You need to weigh the costs associated with what you want to achieve and decide whether to do the tuning yourself or to have a motorcycle shop handle it.

I do not know what a perfectly tuned CBX1000 feels like. I am tuning the FCR because I want to see a state that can be called perfect. After spending time on tuning, fine adjustments through test rides are necessary.

This post covers the part about those fine adjustments. The goal is to keep the jets within a range that allows for fine adjustments throughout the year.

See you again!

CBX1000-写真ギャラリー

In this post, I will focus on photos of the AS air screw from past images related to the FCR. The golden brass part is the air screw. The right side is the main air jet. The main air jet on the right side is generally not adjusted according to tuning manuals.