What causes a lawn mower to idle up and down?

A carburetor that’s incorrectly adjusted is a common cause of poor engine idling that results in hunting and surging. Fortunately, most lawnmowers have two screws that allow you to adjust the carburetor yourself. One screw controls the idle speed while the other adjusts the idle mixture.

How do you fix a surging idle?

Start the engine, then increase and hold the idle speed to 1,000 to 1,500 rpm. Turn the engine off to allow the cleaner to soak into the IAC passageway. Restart the engine, rev and hold at 1,000 to 1,500 rpm, and repeat the cleaning process again.

Why does lawn mower engine pulsate?

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 lawn mower chugging?

Clogged or Dirty Air Filters

Dirty air filters are one of the most common reasons lawn mowers sputter. Dirt can be present in the apertures that lead from the carburetor and the fuel filter and interrupt the flow of fuel supply to the combustion chamber. You want to be sure to clean or replace dirty air filters.

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What causes a carbureted engine to surge?

Incorrect fuel mixture adjustments and engine idling capabilities can be upset by fuel mixture adjustments and fuel vapor recovery system malfunction. The fuel system cleaner added to the fuel tank can open blocked passages in the fuel system that could be causing the surge.

Why does my lawn mower surge at idle?

A carburetor that’s incorrectly adjusted is a common cause of poor engine idling that results in hunting and surging. Fortunately, most lawnmowers have two screws that allow you to adjust the carburetor yourself. … Then slowly adjust the screws tighter or looser in turn until the mower runs and idles smoothly.

What can cause erratic idle?

4 Common Reasons Why Your Engine May Be Idling Rough

  • Vacuum Leak. Most vehicles have a maze of hoses throughout which create a vacuum for both fuel and air. …
  • Spark Plugs. A rough idling engine can be caused by spark plugs or spark plug wires. …
  • Dirty Fuel Injector. …
  • Carburetor Problems.

Can spark plugs cause surging?

The process of surging and dragging. If your vehicle experiences sudden surges of speed, this could be a sign that your spark plugs are dirty or worn. The cause of these surges is that your spark plugs do not ignite the fuel in your engine at the appropriate rate, resulting in an unevenly distributed speed.

Why is my lawn mower not running smoothly?

A dirty air filter is one of the most common causes of a poorly running lawn mower, since it starves the engine of the oxygen needed for combustion. Fuel Filter: Check the fuel filter on the mower to make sure it’s clean, and replace it if needed.

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Why does my lawn mower keep bogging down?

The most common reason why lawn mowers bog down, especially mulching mowers, is grass clippings sticking to the underside of the deck. If your mower packs in too many clippings, there’s not enough room for the clippings to cycle and the blade to keep turning. Fixing this is easy enough, it’s just a messy job.

Why does my lawn mower run sluggish?

Maintenance lapses become evident when the mower turns over slowly or begins to falter at start-up. The fault could be a dirty spark plug, air filter or carburetor, or it could be related to the quality of the gasoline used. Slow starting can also be the result of a failure to clean the blades.