Introduction
Most of the old-generation motorcycle riders have faced the problem of starting the engine in cold mornings, and the choke helped on these occasions. So, what does a choke do on a motorcycle?
If you come across a bad smell while walking on a road, instinctively you block your nostrils by pinching your nose to block the entry of the bad smell either partially or completely. In other words, you are trying to choke your air passages to restrict the entry of the surrounding air mixed with a bad smell.
What this example has to do with a motorcycle choke? Keep reading the article to know.
The choke was a common feature on automobiles that run on carbureted engines viz. motorcycles, scooters, and even cars.
This article takes you through the topics of what does a choke do on a motorcycle and why it is required, do modern motorcycles with fuel-injection engines have a choke, and a few frequently asked questions on the topic.
What does a choke do on a motorcycle and why it is required?
You can define a choke as a manually operated butterfly valve in a carbureted engine and the function of the choke is to restrict (choke) the amount of air entering the carburetor. Less entry of air into the carburetor means an enriched fuel-air mix (more fuel and less air) entering the combustion chamber and this is specifically used when starting the engine in cold conditions. A completely closed choke valve allows negligible air into the carburetor. Without a choke, starting a carbureted engine in cold conditions can be laborious.
We choke our air passage to restrict foul-smelling air entering the nostrils and your motorcycle chokes the carburetor air passage to restrict the entry of air into the carburetor.
Choke valves are butterfly valves located at the upstream side (air filter side) of the venturi, and normally found on automobiles with naturally aspirated carbureted engines; their function is to supply an enriched fuel-air mix when starting an engine in cold conditions. Closing the choke valve (partial to full) produces more vacuum resulting in a higher amount of atomized fuel sprayed from the idle circuit jet into a low amount of air. A manual choke valve is normally operated by pulling a knob conveniently placed near the motorcycle handle or pushing up a lever on the carburetor.
Once the engine reaches the operating temperature, the choke is taken off, and the correct proportion of the fuel-air mixture is controlled by the throttle valve and carburetor.
Some automobiles with a carbureted engine may have automated choke. Here, the choke is operated automatically by sensing the engine temperature. When you attempt to start the engine in cold conditions, the sensor senses the engine temperature and operates the choke to supply an enriched fuel-air mix to the engine and as soon as the engine reaches the operating temperature, the choke is taken off. The design of an automatic choke will be different from a manual choke.
Normally, the function of a choke is to restrict the flow of air into the carburetor/engine, but there may be some chokes that are designed to increase the amount of fuel (instead of reducing the airflow) flowing into the engine. Both designs serve the purpose which is to supply an enriched fuel mix to the combustion chamber.
Before the introduction of fuel injection systems in automobiles, choke valves were found in all automobiles including motorcycles and the chokes were manual or automatic type. Even now you can find choke valves on equipment that use carbureted engines viz. motorcycles, scooters, lawnmowers, marine engines, etc.
One frequently asked question is, if the choke closes the passage of air entry into the carburetor, how combustion can happen without air?
The answer is, the butterfly choke valve may have a small hole in the center to allow little air to be sucked in, and/or there will be one or two additional holes on the air filter side of the carburetor and a small quantity of air is sucked in by the idle circuit through these holes.
Do modern motorcycles with fuel-injection engines have a choke?
Motorcycles with an electronic fuel injection (EFI) system do not need a choke since the EFI system automatically ensures a supply of rich fuel-air mix for starting the engine in cold conditions.
Most of the medium and high-end modern motorcycles come with an EFI system instead of a carburetor. EFI system has computer-like devices (ECU or engine control unit) and sensors to monitor the optimum fuel-air mix for different conditions including starting an engine that is cold due to long time parking. The sensor senses the temperature of the cold engine and the ECU system recognizes the engine temperature and ensures an enriched fuel-air mix is supplied to the engine to help easy starting.
Frequently asked questions (FAQ)
| 01 | What is a motorcycle choke or choke valve? Why a choke is required? |
| A choke valve is a butterfly valve positioned on the air filter side of the carburetor and it is designed to choke (restrict) the entry of air into the carburetor resulting in a rich fuel-air mixture (more fuel and relatively less air) entering the combustion chamber of the motorcycle engine. The rich fuel mix improves the starting-ability of the motorcycle engine which is cold (due to long parking). | |
| 02 | How to operate a manual choke valve? |
| Most manual choke valves are operated by pulling a knob that connects the choke valve through a cable or pushing-up a lever on the carburetor. Do not operate the throttle when the choke is on and remember to push the choke knob or lever to its original position after the engine attains operating temperature. Please look into your owner’s manual to know the position of the choke and how to use it. | |
| 03 | What happens if I forgot to push the choke knob/lever to its original position and ride the motorcycle with the choke in ‘on position’? |
| If you are riding your motorcycle with the choke in ‘on position’, the fuel consumption will be high, the exhaust is bluish (not good for the environment), and increase in deposits in the engine and exhaust. However, there will be no damage to the motorcycle engine. | |
| 04 | Do cars have a choke valve? |
| Cars manufactured till the early 1970s had manual chokes since they ran on carbureted engines. Look into the dashboard of your father or grandfather’s old car, there will be a choke knob. Later, the manual choke was replaced by the automatic choke. This went on till the 1990s when a fuel injection system was introduced to replace carburetors. Most present-day cars have fuel injection systems and do not need a choke. The computer system of the engine gets the input of the engine temperature through a sensor and supplies an enriched fuel-air mix when the engine is cold. |
Conclusion
In the preceding paragraphs, we had a detailed discussion about the choke valve used in automobiles that run on carbureted engines. Hope this article was informative.