Something that can often come up for new bike owners is the challenge of starting a bike in cold conditions. Luckily though, these carburettor engines can combat cold temperatures using a choke valve.
This article delves into the world of choke valves and cables, helping you understand how this benefits motorbikes. This helps enrich the fuel-air mixture, improving the ability to start an engine in low temperature conditions. The ratio of air and fuel required to start the engine changes with temperature due to the physics and thermo-dynamics behind combustion and air density.
On a motorcycle, a choke valve is likely to be a pulling lever either directly attached to the carburettor or indirectly attached to the carburettor via a cable. Our motorcycle cables are to the highest standard and help enthusiasts and professionals alike, get more out of their bikes.
Each model and make of a motorcycle will utilise choke valves and cables slightly differently. Some motorcycles use a choke to reduce the airflow to enrich the mixture, while others use an enrichment valve that increases the amount of fuel as opposed to reducing the airflow.
Both types achieve the same thing but may be set up differently depending on the model and make of bike. Once the engine is in use, and naturally warms up, the choke valve can be closed, to reduce additional fuel being used. Keeping the valve open unnecessarily will lead to poor fuel efficiency. There is no harm using the choke to start an engine. Each bike may implement a choke system in its own unique way.
This will impact how motorcycle owners go about enriching the mixture in the carburettor. At some stage, riders will gain an understanding of how long they need to use the choke to get things going. Again, depending on the temperature, this is likely to vary too. Instead, motorcycle owners should simply be aware of the benefit of using the choke.
If the bike is struggling to start, this is the first thing to try. An alternative to carburettors and something growing in popularity in new bikes is an electronic fuel injection application. This may require some digging, but there could be a few different things going on. Verify that the choke opens and closes and go from there. A malfunctioning choke will also cause excessive fuel consumption. The whole purpose of the choke is to create an enriched mixture.
If the choke is left on or is somehow stuck on, the enriched mixture will continue to be produced. Even over a relatively short period, like minutes, fuel consumption is drastically reduced. There should also be an effect on engine performance due to the restricted airflow. Excessive fuel consumption will also produce excessive smoke out of the tailpipe. This smoke is unburned fuel escaping into the atmosphere.
At startup, there may be a bit of exhaust smoke, but a prolonged amount is indicative of a problem. This may also cause backfiring out of the exhaust.
It is also possible to have backfiring occur through the air intake. A backfire through the carb is most likely indicative of a lean mixture. The uneven burn of a lean condition can carry ignition back through the opening intake valve and into the carburetor. This can be caused by the choke opening too early before the engine is warmed up. This can be reinforced when the engine stalls right as you open the choke. However, the fact that the engine runs with the choke on proves that the choke is working.
This problem is probably more likely due to a restriction blocking fuel from getting into the carburetor. If the choke is malfunctioning, it may be due to the linkage being out of adjustment. The cable has threaded adjustments to tune the opening and closing of the choke. There are return springs that will pull against the cable, so a bad cable could keep slipping out of the selected position.
Sometimes the cable can stick or even seize making it difficult to operate. It is possible to replace the choke plate and other components, but it requires disassembling the carburetor. However, some components can be replaced. The most common is the choke linkage. This is usually a lever and cable or a spring-loaded plunger. These are the mechanisms by which the rider can control the choke. In the case of an electrically controlled choke, there is a solenoid that can short internally and can also be replaced.
Replacing the choke linkage will typically require gaining access to the carburetor. If your motorcycle has body panels that enclose the carburetor, start by removing those as needed. Carburetors that are powered by an electric heating element may experience a loose wire or ground connection, which eventually prevents the choke from opening.
The choke can be adjusted to change the temperature at which the opens and closes, which results in a lean fuel starting mixture. You can adjust the choke by loosening the screws that hold the housing and the choke on place and then rotating the housing.
On many newer model vehicles, rivets are used instead of screws, and can easily be replaced after the adjustments are made by drilling them out. It is important to pay attention to the rate at which the choke opens and closes. Contrarily, if the choke opens too quickly in cold weather, it may cause the engine to stall or not start altogether. The rate at which the choke pulls off plays a critical role at which the choke opens and closes especially during warm weather.
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