The choke is a plate in the carburetor that opens and closes to allow more or less air into the engine. Similar to the throttle, the choke plate rotates from a horizontal to vertical position to open up the passageway and allow more air to get by. The choke is located before the throttle, and manages the total amount of air going into the engine.
The choke is only used when starting a cold engine. When doing a cold start, the choke should be closed to limit the amount of air going in. This increases the amount of fuel in the cylinder and helps to keep the engine running, while it is trying to warm up. Once the engine has warmed up, a temperature sensing spring slowly opens the choke plate to allow the engine to breath fully.
If you are having trouble getting the car started in the morning, inspect the choke on your engine. It may not be completely closed on cold start, allowing too much air into the cylinder, in turn preventing the car from idling correctly. Once the car has warmed up, if the choke does not open fully, the restriction in air may result in reduced power.
Part 1 of 1: Inspect the choke valve
- Carburetor cleaner
- Safety glasses
Step 1: Wait until morning to check the choke. Check the choke and see if it is closed when the engine is cold.
Step 2: Remove the air filter. Locate and remove the engine air filter and housing in order to access the carburetor.
This may require the use of hand tools, however, many times the air filter and housing are secured using only a wing nut that can often be removed without using any tools.
Step 3: Check the choke valve. The choke valve will be the first butterfly valve you see when removing the air filter. This valve should be closed because the engine is cool.
Step 4: Step on the gas pedal a few times. Press the gas pedal a few times to close the valve.
If your car has a manual choke, have someone move the lever back and forth while you watch and see if the choke valve moves and closes.
Step 5: Try moving the valve slightly with your fingers. If the valve refuses to open or close then it could be stuck shut somehow, either from dirt build up or due to an improperly functioning temperature sensing adjustor.
Step 6: Use carburetor cleaner. Spray some carburetor cleaner on the choke and then wipe it down with a rag to clean out dirt.
It is safe for the cleaner to go inside the engine so don’t worry about wiping every last bit of cleaner.
Once you close the choke, reinstall the air filter and housing onto the carburetor.
Step 7: Run the engine until it warms up. Turn on the ignition of your car. Once the engine is warm, you can remove the air filter and check whether the choke is open or closed. At this point, the choke should be open to allow the engine to breathe fully.
- Warning: Never start or accelerate the engine with the air cleaner removed in case of a back fire.
When you inspect the choke, you also get a chance to look inside the carburetor. If it’s dirty, you might want to consider cleaning out the whole assembly to keep the engine running smooth.
If you are having trouble identifying the cause of your engine troubles, get a certified technician from YourMechanic to inspect your engine and determine the cause of the problem.
This article originally appeared on YourMechanic.com as How to Check the Choke on a Carbureted Engine and was authored by Spencer Cates.