Repairs on lawn mowers are often fairly straightforward since they’re visible from general wear and tear, or they appear in the maintenance section of your manual. But, when it comes to repairing a carburetor, you need to know a bit about engines and understand the symptoms to watch out for. This being said, diagnosing a bad carburetor isn’t actually too difficult once you know what you’re looking for.
How to Spot a Bad Lawn Mower Carburetor (The Short Answer)
When a carburetor goes bad, it will affect the fuel and airflow to the cylinder. This can include stopping fuel, starving fuel, providing too much fuel, and incorrect fuel to air mixture. As a result, lack of power, poor idling, black smoke, and not being able to start the engine are a few symptoms you should look out for.
How to Tell if Your Lawn Mower Carburetor is Bad (Common Symptoms)
If you have been around lawn mower engines as long as I have, you start to notice that the common symptoms of a struggling lawn mower are pretty similar to one another.
Because of this, it can be challenging to figure out where the problem lies. So let’s look through the symptoms and figure out how to tell if your lawn mower carburetor is bad.
Engine Won’t Start
If your engine simply won’t start, then there’s a good chance it’s due to the carburetor. The choke reduces airflow into the carburetor without affecting fuel volume. This is perfect when trying to start a cold engine. The problem is that when it malfunctions, you’ll have a problem starting either when it’s cold or warm.
Engine Doesn’t Idle
If the engine struggles to idle and wants to stall, then there could be an issue with the idler and the choke. These components control the fuel mixture to get the engine started and allow them to rest at idle speed. As soon as this mixture ratio is wrong, the lawn mower will not idle correctly.
Jerky Engine & Back Firing
If your engine appears to be jerky when running, then it’s probably running lean. This is when the concentration of air to fuel is too high. You’ll also get the occasional backfire when the fuel ignites in the exhaust chamber.
Surging & Spluttering
Opposite to a lean fuel mixture is a rich fuel-to-air mix ratio. This is when there is too much fuel in the mix ratio. A rich mix makes the engine surge and splutter when in use. This is usually caused by the carburetor pushing too much fuel into the cylinder head’s combustion chamber. A rich mix needs more effort to clear the fuel, resulting in a lag in power and poor engine performance.
Engine Doesn’t Accelerate
Once you increase the throttle on your engine, the carburetor should increase the fuel/air mixture to the cylinders. Any number of the components in the carburetor could be broken or damaged if this increase isn’t achievable.
Getting too much fuel at once through the carburetor will cause the engine to flood. Gasoline is vaporized in the carburetor and then fed into the cylinder where the spark plug ignites the vapor. If fuel is provided as a liquid and not vapor, then it will lead to a problem in the carburetor operation.
If the carburetor runs excessively lean, you will see black smoke blowing from the exhaust pipe. Black smoke means the carburetor is having a difficult time reaching the correct mix ratio.
Excessive Fuel Consumption
A lot of the symptoms of a bad carburetor are a result of too much fuel. For example, running the fuel mixture lean affects how much gas you use to cut your lawn. I know I should only use one tank of gas to cut my lawn. So, if my mower runs out of gas before I’ve finished, I know there’s a problem.
Carburetors have several seals in the form of o-rings and gaskets. These are there to keep unwanted air out and allow the operator to make tiny adjustments. If you find that you have fuel leaking from one of these seals, your engine will have trouble since the fuel/air mixture is affected.
Putting the Signs of Bad Carburetor on Your Lawn Mower Together
Now you know there are many ways to tell if your lawn carburetor is bad. Unfortunately, you’ll probably experience more than one of these symptoms at the same time. So, you’ll have a clearer idea that you’ve got a bad carb once you start putting the symptoms together.
In my experience, getting the carburetor fixed or replaced as soon as possible is best. These symptoms can lead to bigger engine problems, which could eventually mean you’ll have to replace the mower altogether if you’re not careful. Yikes!