What causes a lawnmower engine to rev up and down?

A lawnmower that hunts and surges may be experiencing something as simple as an airflow issue. If the air that the engine requires to run is blocked, especially sporadically, it can cause the engine to slow down. When the blockage moves or clears, the engine may suddenly rev up in response.

What causes lawn mower engine surging?

The most common reason for a surging lawn mower engine is a blockage in the fuel supply, but there are other possibilities: Bad gas. Bad spark plug. Dirty / faulty carburetor.

Why is my Briggs and Stratton surging?

The mower is surging/hunting because the carb is dirty. The main jet needs to be cleaned. You may be able to clean the carb without removing the carb. There is a main jet at the bottom of the carb that retains the fuel bowl.

How do I fix my lawn mower surging?

Inspect the vent on your gas tank’s cap and clean it if it’s dirty. Drain the gas tank, clean the gas bowl, and add a fresh batch of fuel. Or you can inject fuel cleaner to clean the fuel line. After changing the fuel or injecting fuel cleaner run the lawn mower as usual.

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What does engine surging mean?

Engine surging is when an engine starts easily and accelerates smoothly, however after a few minutes at a steady speed, it either surges in speed or misfires. Misfiring happens when one of the cylinders of an engine’s combustion cycle fails.

How do you adjust the governor on a Briggs and Stratton engine?

First, loosen the arm until it is moving freely. Next, open the throttle to full capacity while making a note of which direction the arm moves in when the throttle moves through it. Once the throttle is fully opened, move the governor shaft in the same direction the governor arm traveled.

What causes surging in a small engine?

Carburetor Issues

A dirty or gummed up carburetor causes an engine to surge. … Serious problems — such as damaged gaskets, broken jets or internal parts that will not come clean — require the installation of a carburetor kit or a carburetor replacement.

How do you adjust the idle speed on a Briggs and Stratton engine?

How to Adjust the Idle on a Briggs & Stratton Lawn Mower

  1. Loosen the set screw in the center of the air filter with a flathead screwdriver. …
  2. Tighten the idle adjustment screw, found on the side of the carburetor, by turning it clockwise just to the point where you feel it lightly touching the seat of the carburetor.

How do you know if your ignition coil is bad?

One of the symptoms of a bad lawn mower ignition coil appears when you are mowing the lawn and the mower gets hot and literally shuts off. The mower must cool down over a period of time and will start and run for awhile until it gets hot again, at which time it will shut off again.

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Why is my mower surging at full throttle?

If your lawnmower’s engine is surging it could be a problem with the carburetor. The carburetor mixes air and fuel to the perfect ratio for combustion. There are passages and nozzles (called jets) that route the fuel through the carburetor. … The main jet supplies fuel to the engine when it is at full throttle.

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