Prior to the 1990s, the process of starting a car on a cold morning would have likely involved a manual choke. The choke, a small valve located in the engine’s carburetor, plays a key role in limiting the air intake to the combustion chamber of the engine, allowing the engine to start and run more easily. With the rollout of electronic fuel injection systems, the manual choke passed into history.
Here’s a breakdown of this feature for any mechanic working on an older vehicle that features it.
What Is a Manual Choke, and What Role Does it Play in the Running of a Vehicle’s Engine?
The choke consists of a small plate located within the carburetor housing. The purpose of this plate is to control the flow of air into the engine. This plate can be manually rotated from a horizontal to a vertical position via the manipulation of a choke lever in the car’s interior. Pulling out the choke will put it in a horizontal position—cutting off the air intake to the engine and ensuring a more fuel-rich environment within the combustion chamber. This in turn will allow the engine to “catch”, run continuously, and warm up more easily.
A manual choke is primarily used in cold start situations, when the engine has been off for several hours and has been subject to cold temperatures. This is often the case when cars are parked outside, in driveways or parking lots overnight. The concept of “warming up” a car would often involve allowing the engine several minutes to idle with the manual clutch closed, before taking to the roads with optimum engine temperature having been achieved.
Recognizing the Range of Choke Levers You Might See During Your Automotive Career
Veteran pros with an automotive career will know that a huge range of choke levers were produced and installed in vehicles over the decades. They can range from small, pull-and-push knobs (found in the Dodge D Series), to plastic levers located near the steering column (seen in the Volvo 240), to metal levers located on the interior floor (which you might see in the Fiat 500).
Using a choke would involve pulling the lever out to its fullest extent—thus closing off the airflow—while gently pressing on the gas pedal to produce revs. The choke would then be partially closed over the course of a minute or so of this process, before returning to its original position when the engine is warmed up, put in drive, and driven away. Some variation may take place between vehicles, with later carburetor-equipped vehicles providing an increasingly simplified experience.
Common Manual Choke Issues That Pros With Auto Repair Training Will Encounter
Due to the fact that most vehicles that feature manual chokes are at least a few decades old by now, it’s not uncommon for vehicles that have them to exhibit engine issues. The challenge for the professional with auto repair training is to ensure that any observed problem is actually with the choke, and not related to the throttle or adjacent component in the engine.
Given that the plate is located within the engine compartment, the issue of dust and grime building up and affecting the plate’s motion can arise, with dirt preventing the horizontal-to-vertical motion. In inspecting a choke, a professional should carefully remove any protective cover or filter, inspect the plate’s action, and use carburetor lubricant or compressed air to clean out any buildup of dirt. Given that many older chokes are connected to the controlling lever by a manual wire line, replacing this element will resolve any issue related to a frayed or snapped line.
Mechanics will find elements such as automotive temperature sensors, which “run” the choke without the need for human interaction, will be more common the more modern the vehicle is.
Do you want to become a knowledgeable auto professional?
Contact CATI today to find out about the best courses to kick start your auto mechanic career.
