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If you have ever tried starting a cold engine, you will know that it won’t easily start. This is especially true of carbureted engines such as those used in motorcycles. Here is where the choke comes in.
How does a motorcycle choke function? To help the cold engine start, the choke delivers an enriched mixture of air and fuel. The cold engine starts when it has a rich fuel to air ratio. A higher ignition rate is achieved when there is more fuel in the cylinder. After the engine is warm up, the choke can be removed.
While each choke’s design is unique, there are common elements that all chokes share.
How the Choke Works
First, the plate restricts airflow upstream of the throttle plate. It may seem counterintuitive to restrict the engine’s airflow, as an engine requires air to ignite. If there is a controlled restriction, however, the engine can be enriched by fuel. The choke creates more vacuum, which pulls more cold fuel vapors into low volumes of air.
Second, fuel must be sourced from an alternative channel to the main carburetor. A well with fuel is usually located next to the float box. The choke is able to function without the input of the throttle because it has its own fuel source. The throttle plate is also closed so that the engine creates more vacuum, which in turn draws more fuel.
As the engine heats up, the importance of the enriched mix decreases. The correct fuel mixture will make the engine perform better. As the engine heats up, the throttle should be slowly back-off. Once the engine is at its operating temperature, the throttle plate or carburetor regulates the fuel mixture.
Some carburetors are equipped with automatic chokes, which allow the engine to warm up and reduce the choke. The choke plate is controlled by a metal coil. Some designs heat the metal coil using the heat from the engine or exhaust. The heat from the engine or exhaust causes the coil to expand, spinning and opening its choke.
Some chokes use electricity for heating the coil. This can be controlled a little more precisely. Some choke designs can be tied to the throttle control, so that the plate opens with throttle application.
Signs Your Choke Is Not Working
Here are some signs that your choke is not working properly:
- It is hard to start
- Excessive fuel consumption
- Excessive smoke from the engine running
- Turning the carburetor on or off
- Start engine, then stalls
If your engine has trouble starting even though it is in operation, there is something wrong. It may take some digging to find the problem, but it could mean that there are several other things. Either the choke isn’t closing enough or the fuel is being stopped. Check that the choke is open and closed.
An improperly functioning choke can also lead to excessive fuel consumption. The choke’s purpose is to produce an enriched mixture. The enriched mixture can be created even if the choke has been removed. Fuel consumption is dramatically reduced even if it’s only for a short time, such as 10-20 minutes. The restricted airflow should also have an impact on engine performance.
Excessive fuel consumption can also lead to excessive smoke coming out of your tailpipe. This is the smoke from unburned fuel that escapes into the atmosphere. While there might be some exhaust smoke at startup, it is not indicative of a problem. The exhaust could also backfire.
You can also have backfiring through the intake. If the carb backfires, it is likely that it is a lean mixture. A lean mixture can cause an uneven combustion and lead to ignition going back through the intake valve into the carburetor. This can happen if the choke is opened too soon before the engine heats up.
If you are having a problem with the engine starting, then immediately stalling, you might be tempted to think that the choke isn’t working. The engine may stall as soon as you open it.
The fact that the engine runs without the choke on is a sign that the choke works. This is likely to be more common due to fuel restriction that prevents fuel from entering the carburetor.
It could be that the linkage is out of adjustment. To adjust the opening and closing of choke, the cable has threaded adjustment. Sometimes the cable can be stretched out and then the adjustment won’t work effectively.
The cable can be pulled against by return springs, which could cause the cable to slip out of its chosen position. Sometimes, the cable may stick to or seize making it hard to use..
How to fix or replace the choke
Since the choke is typically integrated into the carburetor, it isn’t usually a replaceable component. However, it is possible for the choke plate to be replaced. This requires disassembling of the carburetor. So it isn’t likely that you will need to replace the choke.
However, certain components can be changed. Most common is the choke connection. It is typically a cable and a lever, or a spring-loaded plunger. These are the mechanisms through which the rider can control choke. An electrically controlled choke has a solenoid which can be shorted internally and can be replaced.
Most likely, you will need to access the carburetor in order to replace the choke lineage. Start by removing any body panels that surround the carburetor of your motorcycle. The bike’s design may require you to take out the air cleaner. On certain designs, the carburetor may need to be removed. Get to know your bike’s needs before you start making preparations.
It is easy to replace the cable. You may need to loosen a few threaded fittings from the handle and choke sides. If you have the replacement part on hand, make sure it is the same length as a cable that is too long or short won’t work.
After the link has been replaced, attach any pieces that were previously removed. Before you start the bike, test the cable by activating it. If the choke is not working, you can try to start it up and turn it on.
Choke lever arm can also be damaged. The arm replacement process is similar to that of the cable linkage. The depth of the project is dependent on the specific design of your bike’s carburetor, so study up before tearing into it.
How to Make Your Choke Last Longer
The choke can cause wear and tear but will alert you to any maintenance needed. The choke cable can become unusable over time if it is not used often. It is possible for the choke plate to become clogged up and cause problems. These problems are usually easily fixed.
WD-40, or any other penetrating oils can be used to repair a stuck link or cable. To do this, you need to reach the point where the cable connects to a choke plate. Spray the cable and activate the choke to allow the grease to reach the joint. Lubricating these points regularly will prolong the life of your choke.
Carburetors are prone to becoming dirty. Keep your air filter clean. It’s a good idea for your motorcycle to be cleaned if it has any of these issues.
If you aren’t into disassembling the carburetor and cleaning it, there are spray cleaners available that can help a bit. Some products need to be cleaned while the engine is still running, so they can burn and become exhausted.
The choke should not be a high-maintenance item.. It may wear faster if it is used frequently, but the constant presence of gasoline can help keep it clean. Make sure that when storing the motorcycle for winter you drain the fuel and make other preparations so that the fuel system doesn’t get gummed up.
When the engine is cold, it is more difficult for fuel to be burned. The choke design allows for an enriched mixture of air and fuel to be delivered to the combustion chamber even in cold conditions. After the engine starts, the engine warms up. It is easier to ignite the fuel, so the choke is slowly opened.
Pay attention to your engine’s startup and idle condition as this may be indicative of a choke malfunction. For a longer life expectancy, keep the linkage well lubricated.