Quick Answer: Lawn Mower Engine Surges When It Is At Full Throttle?

What causes a small engine to rev up and down?

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. To fix this type of problem, check the air filter to ensure that it’s not clogged with dirt and debris.

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.

What causes a carbureted engine to surge?

If an engine is not getting enough fuel (this is called “running lean”), due to fuel pressure (regulated by the fuel pump and regulator), restricted fuel injectors, a vacuum leak or really anything that throws off the fuel mixture going in to the engine, this can cause the surge.

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Why is my mower engine surging?

This vent is just large enough to allow air into the tank, creating enough backpressure to aid in fuel delivery to the carburetor. 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.

How do I adjust the governor on my small 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.

What does engine surging mean?

Surgingdoes not refer to a knocking engine or one that idles rough or stalls. 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.

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.

What causes a snowblower engine to surge?

If the snowblower engine RPMs are surging up and down, check the following parts for damage: springs, gasket, carburetor, and spark plug. There are springs on the carburetor that allow the butterfly valves to open and close properly. The springs also ensure the governor is operating properly.

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How does the governor work on a Briggs and Stratton engine?

To control engine speed, a mechanical governor uses gears and flyweights inside the crankcase to detect changes in the load and adjusts the throttle accordingly. This closes the throttle, limiting the air-fuel released into the engine. When the engine load increases, the crankshaft spins more slowly.

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 an idle surge?

The cure for this condition is to clean the valve with some aerosol throttle cleaner or engine top cleaner. Here’s how to clean the IAC valve: Disconnect the air intake ductwork from the throttle body. Start the engine, then increase and hold the idle speed to 1,000 to 1,500 rpm.

What causes RPM to fluctuate while idling?

Why does my engine’s RPM seem to fluctuate (runs rough)?



Many engine performance problems can be linked to maintenance issues such as stale fuel, dirty air filter, fouled spark plug, and deteriorated oil. Engine hunting and surging at idle is usually caused by a fuel delivery, air leak, or governor system problem.

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