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?

Surging is also caused by water that got into the fuel. A mower left in a heavy rain or condensation on a hot summer day can choke the engine. Empty the gas tank, properly dispose of the old fuel and try a fresh batch of gasoline.

How do I stop my lawn mower from 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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Why is my Briggs and Stratton 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.

What causes an engine to hunt and surge?

Engine hunting and surging at idle is usually caused by a fuel delivery, air leak, or governor system problem. Cleaning/overhauling the carburettor, adjustment of the governor, and/or changing the air filer may be required.

Can spark plugs cause surging?

3. Surging and Lagging. Another good indication that your spark plugs are dirty or worn is if your vehicle experiences surges of speed, resulting in a jerking acceleration. These surges occur because your spark plugs are not igniting the fuel in your engine at the proper rate, resulting in an uneven speed.

How do you fix a surging idle?

Turn the engine off again, and reattach the air intake duct work to the throttle body. Start the engine and rev and hold to 1,500 to 2,000 rpm until no white smoke is coming out of the exhaust pipe. Cleaning the Idle Air Speed Control Valve with aerosol throttle cleaner can often solve an idle problem.

How do you adjust the idle on a lawn mower?

How do you adjust the idle on a 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.
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Why does my lawn mower keep bogging down?

Excessive dirt and grass can clog the air filter system or the cooling fins, which will lead to power loss and hence bogging down of the mower under load. The fuel system also gets clogged with excessive dirt.

How do you adjust a carburetor on a lawn mower?

Set the throttle to fast and start the mower engine. Turn the high speed screw first clockwise until the engine slows, then counterclockwise until it slows. Locate the center point where the engine idles best. Move the throttle from slow to fast then back to slow to test the adjustment.

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

To adjust the governor, you would loosen the screw on the bottom of the governor arm and push the governor arm so the throttle is wide open. Then you would turn the bottom “clip” (which is connected to the governor shaft) counter clockwise. This will set the governor shaft on top of the governor spool.

How do you adjust a Briggs and Stratton carburetor?

Locate the idle adjustment screw on the side of the carburetor. It sometimes has a spring wound around the shaft. Turn this screw clockwise with a Phillips screwdriver until you encounter resistance, which means it has contacted the carburetor seat. Back it off 1 to 1 1/2 turns.

What does it mean if your RPM go up and down?

Hi There, It sounds like you may have a dirty or failing idle air control valve causing your engine idle to fluctuate. … When this happens, the job of the idle air control valve is to bring this deceleration down to a slow and smooth idle rather than suddenly cutting off the fuel supply causing the motor to die.

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Can a faulty oxygen sensor cause engine surging?

Oxygen sensors are among the most interesting and important sensors on your engine. … Surging is among the many problems a failing O2 sensor can cause, but it isn’t the only one.

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