With the FCR, you can start the engine even on early winter mornings.

The summers in Hiroshima, where I live, are hot. In winter, although the roads don’t freeze, it’s too cold to feel like riding a motorcycle. A few times a year, we even get snow. I’m going to write about starting the engine of a carbureted motorcycle on early winter mornings.

Let’s focus solely on winter starts with a carburetor. Normally, if you think about it, old newspaper delivery Honda Cubs would start easily with the choke and a kick. This means the engine can start even on early winter mornings.

Next, let’s talk about motorcycles equipped with an FCR carburetor. There’s no choke. Instead, you twist the throttle about three times to use the accelerator pump as a substitute for the choke. After waiting for about 10 seconds, you start the engine with the starter motor. The engine starts normally, though the idle might feel weak and unstable. Once the engine starts, you slightly open the throttle to prevent it from stalling.

Some people only ride their bikes on weekends for fun, or maybe just once a month. If you ride your FCR-equipped bike daily for commuting, you won’t have any issues to worry about. But for those who don’t ride often, starting the engine on an early winter morning might make you a bit hesitant. Don’t worry though, the engine will start even on those cold mornings.

From the next section, I’ll go into more detail about the engine startability of the FCR in winter. However, I won’t go into super detailed stuff like how tuning can affect startability. I’ll be covering the basics. Winter starts are something you get used to. Being used to starting your bike in winter means you’re riding it nearly every day of the year.

Most large motorcycles equipped with FCR carburetors are purely hobby bikes, ridden mainly on weekends. This content is meant for those who may feel a little anxious about starting their engine in winter. So, let’s get started!

How to Start a Motorcycle with an FCR Carburetor

In both summer and winter, start by twisting the throttle 2 to 3 times to release fuel from the accelerator pump before starting. In winter, after twisting the throttle, you should wait about 10 to 30 seconds for the fuel to vaporize (atomize).

When you turn the starter motor, the engine will start up easily. The trick is not to open the throttle until you feel the engine’s initial combustion (the first ignition). Once you feel that initial combustion, then you can adjust the throttle to prevent the engine from stalling.

It’s harder to start the engine when the battery is weak than in winter conditions.

The most difficult time to start the engine is when the battery is weak. A weak battery during winter is the worst-case scenario. If you keep cranking the starter motor, the voltage will gradually drop. It also makes you worry that the spark plugs might overheat and melt.

I’ve never personally experienced any trouble from overusing the starter motor, but I feel that if you crank it excessively, things like the spark plugs or battery terminals could potentially melt. Since it's a cold start, there might be some minor damage to the engine. If the battery voltage drops too low, it's game over.

Sometimes, if you give it some time and try again, you can at least reach the first ignition (initial combustion). However, if you can't get that initial combustion after waiting a bit, recharging the battery is necessary.

Battery Inspection and Maintenance

It's also important to check for rust around the battery terminals and wiring, as it can create resistance. Cases of poor starting performance can sometimes be caused by rust that isn’t easily visible. Additionally, there are instances where stainless steel bolts mistakenly mixed in can create resistance and melt.

1. Check Battery Voltage: Use a multimeter to check the battery's voltage. Ideally, a fully charged battery should read around 12.6 to 12.8 volts when the engine is off. If the voltage is below this, the battery may need charging or replacement.

2. Inspect Terminals: Ensure the battery terminals are clean and free of corrosion. Corrosion can cause poor electrical connections, making it difficult to start the engine. Clean any corrosion with a wire brush or terminal cleaner.

3. Check Terminal Connections: Ensure that the terminal connections are tight. Loose connections can result in voltage drops and trouble starting the engine.

4. Check for Leaks: Inspect the battery for any signs of leakage. If you notice any fluid leaking from the battery, it’s a sign of internal damage, and the battery should be replaced immediately.

5. Test Battery Under Load: If possible, use a battery load tester to check how the battery performs under load. A weak battery might show good voltage when not in use but fail under load.

6. Inspect Wiring and Fuse Box: Check the wiring around the battery for any frayed or damaged wires. Also, ensure that all fuses are in good condition, as a blown fuse could prevent the starter motor from functioning properly.

7. Charging: If the battery voltage is low, charge it using a battery charger designed for motorcycle batteries. Avoid using chargers with too high an output, as this can damage the battery.

Regular inspection of these points can help ensure reliable engine starts, especially in colder weather.

In the case of fouling the spark plug

What does it mean for a spark plug to be fouled? It refers to a state where the plug becomes damp and fails to create a spark. When you continuously fail to start the engine, unburned fuel adheres to the spark plug. Carbon buildup can also occur, causing the plug to feel moist.

Once a spark plug is fouled, it is said to be difficult to ignite. However, if you allow it to dry properly, it can still produce a spark. Of course, if the spark plug has been in use for a long time, it’s advisable to replace it at this point.

When you feel that the plug is fouled, it usually comes after cranking the starter motor excessively. In such cases, it’s best to give up for the moment and consider recharging the battery, as well as replacing or maintaining the spark plug.

Can FCR Tuning Improve Starting Performance?

In early spring, I have experimented by adjusting the pilot screw every morning to see if there was any change in starting performance. I found that there is indeed a change in starting performance. I tried moving the pilot screw 90 degrees every 15 minutes.

When the starting performance is optimal, the engine tends to run rich once it warms up. This leads to a situation where you have to prioritize either starting performance or the ideal idle speed at operating temperature.

Outside of winter, I rarely encounter issues with engine starting. If you're struggling to start the engine in early spring, it could indicate that fuel isn't reaching the engine properly, suggesting problems outside of the carburetor.

This discussion specifically pertains to winter conditions. It's important to note that starting performance was not an issue in the fall. It might be beneficial to turn the pilot screw slightly richer about 15 minutes before starting the engine.

Ultimately, the accelerator pump is used to add fuel. You don’t need to worry too much about tuning for starting performance at first.

Behavior of the Air-Fuel Ratio Gauge

Behavior of the Air-Fuel Ratio Gauge Immediately After Engine Start

Immediately after starting the engine, the air-fuel ratio (AFR) can fluctuate significantly, often showing values like 17 or 14. These readings can be heavily influenced by engine RPM, so they are not very reliable during this period. Even in the fall, the AFR immediately after starting tends to be in the 14 range.

Once the engine warms up, the idle becomes stable around an AFR of 13. It’s important to note that just because it’s winter, the stable air-fuel ratio doesn’t change drastically. The stability of the AFR is relatively consistent across different seasons.

Tuning Considerations for Winter

I don’t think there are many issues that would cause performance to worsen. The basic principle of winter tuning is to enrich the fuel mixture. In my opinion, if the bike was running well in the fall, there shouldn’t be any major concerns.

Often, after making adjustments to the jets, you can feel a noticeable improvement in performance. For example, changing the main jet by about 10 numbers, such as from 125 to 135, can lead to a significant enhancement in engine performance. This improvement is not only evident at full throttle but also affects performance at around half throttle.

Adjusting the clip position by one notch to a richer setting can also enhance performance. For the slow jet, you usually don’t need to change it; simply adjusting the air screw is often sufficient.

Even in Sub-Zero Temperatures, Engine Idle Stabilizes Once Warmed Up

Whether You Can Ride Comfortably on a Motorcycle is Another Matter

Even if snow is piled up, the engine will stabilize at idle as long as it warms up. This means that the idle can be stable under cold conditions. However, this does not take into account whether you can actually ride the motorcycle. If you're looking to perform a snow attack, it should be possible. I can't say how low the temperature can drop before the FCR carburetor faces challenges, though.

Cold Weather Improves Motorcycle Performance

While This Discussion on Winter Starting Performance Might Be Slightly Off-Topic, Motorcycles Tend to Perform Better in Winter

Motorcycles often run better in winter. This could be related to the engine cooling down and the surrounding temperature of the carburetor. Even when riding on paid highways, you can feel the improved performance of the motorcycle. For example, the oil temperature of the CBX1000 drops quickly even after exceeding 100 degrees Celsius in winter conditions.

With the FCR, you can start the engine even on early winter mornings.【summary】

Extreme Tuning for the FCR Should Be Avoided

When it comes to tuning for extreme cold or scorching heat, there are some considerations to keep in mind. In extreme heat, no matter how much you open the air screw, the motorcycle often feels very unstable. While you can achieve a tuning level that seems acceptable, it rarely feels perfect. The next day, you might notice something feels off.

On the other hand, riding in winter when the roads are icy can be dangerous. I have never tuned a motorcycle for extreme cold conditions. However, when tuning the FCR in situations where the roads are not frozen, it seems like the air is denser, allowing for a more enjoyable tuning experience. Riding in these conditions can be very fun.

That said, it can get so cold afterward that it might negatively impact the human body. Please be cautious of road conditions and freezing.

See you again!

CBX1000 – Photo Gallery

I will publish a photo of the air-fuel ratio gauge installed on my CBX1000 from my past logs.