How to Know if Your Carburetor Is Failing

A carburetor regulates the mixture of air and fuel sent to your engine to be ignited in the cylinders and provide power. Carburetors were widely used until the 1980s, when fuel injection and electronic engine control systems were introduced to improve fuel efficiency and drivability, as well as to lower emissions.

If you own an older vehicle that was made before the age of fuel injection arrived, it probably has a carburetor, or possibly more than one. Carburetors can get out of whack pretty easily. Here’s how to know if yours needs an adjustment or replacement.

What are the symptoms of a bad carburetor?

Most carburetor problems can be diagnosed by looking at the type of problem your engine is experiencing.

Hard starting: If your older car is reluctant to start when the engine is cold, it could be that the air-fuel ratio is out of whack. This could be an adjustment issue, or the choke mechanism could be stuck all the way open, resulting in too lean of a fuel mixture for the engine to start.

Rough or fast idling: If your car starts fine but doesn’t idle smoothly and at a normal speed, this can point to a different type of carburetor issue.

Rough idling causes the engine to idle too slowly, shake or sputter when you take your foot off the gas. This is usually a sign that your engine is getting an incorrect air-fuel mixture — either to rich or too lean could cause a rough idle.

If the engine is idling too fast, it’ll feel like it’s revving too high when you take your foot off the accelerator. This usually happens either because the choke is sticking, or the idle speed needs adjustment.

Stalling: If your engine stalls when you’re not pressing on the gas pedal, your carburetor may not be supplying enough fuel, or perhaps the idle is set too low.

Hesitation: If your carbureted car hesitates or stumbles when you need to accelerate, it’s usually caused by insufficient fuel getting through the carburetor and into the engine when you need it most.

Poor fuel economy or black smoke from the exhaust: If you’re getting bad gas mileage, it could be a sign that your carburetor is letting more fuel than necessary into your engine. In extreme cases, there’s so much extra gas that some of it can’t be burned in the cylinders. Instead, it may come out your exhaust pipe as thick, black smoke. This condition can damage your spark plugs, waste your gas and money, and cause a great deal of air pollution.

What to do if you have a bad carburetor

Unless you are an extremely experienced mechanic, dealing with a bad carburetor may be beyond your abilities. Trying to fix a bad carburetor without the proper knowledge can make things worse.

If your car is experiencing any of the above issues, take it to a repair shop that is familiar with older, carbureted cars.

How does a carburetor work?

All cars that run on gasoline, whether carbureted or not, depend on the proper mixture of gasoline and air getting into the cylinders. The carburetor acts as a metering valve, mixing the gasoline with the air that passes through it as the engine runs.

To accelerate, you push on the gas pedal, which increases the airflow through the carburetor, pulling more gasoline with it and providing the power you asked for. To slow down, you ease up on the gas pedal, which reduces the carburetor’s airflow, so it pulls less gas through, creating less power.

A carburetor is a complex device. It has a choke mechanism that makes cold starting easier. It also has a float valve, similar to the one in a toilet, that maintains a consistent level of fuel within the carburetor. A carburetor is like a mechanical jigsaw puzzle, with narrow passages that can get clogged, linkages that can get stuck, and rubber and plastic parts that can deteriorate and malfunction.

Later automotive carburetors often had crude emissions controls attached, which gave them a reputation for reduced performance and poor drivability. The advent of fuel injection eliminated these issues, and automotive carburetors became obsolete technology.