Small Engine Trouble Shooting Guide

Small engine trouble shooting can be a real pain in the muffler. Small engine problems can be caused by an a several different issues. There is no clear black and white only different shades of gray.

To assist in repairing your small engine we’ve created this DIY small engine trouble shooting guide. If you have questions or comments please feel free to contact us using the comments section below or our contact form.


ENGINE CRANKS BUT WILL NOT START

  • Empty fuel tank.
  • Fuel shut off valve closed.
  • Fuel line clogged.
  • Dirt or water in fuel system.
  • Spark plug lead loss or disconnected.
  • Ignition switch or kill with in OFF position.
  • Transmission not in neutral.
  • Spark plug failed.
  • Spark plug improperly gapped.
  • Ignition module malfunctioning.
  • No or low compression.

ENGINE STARTS BUT WILL NOT KEEP RUNNING

  • Fuel tank vent plugged.
  • Dirt or water in fuel system.
  • Choke cable malfunctioning.
  • Throttle cable malfunctioning.
  • Loose wires or connections that short kill terminal of ignition.
  • Carburetor not adjusted properly.
  • Cylinder head gaskets malfunctioning.
  • Fuel pump malfunctioning.

ENGINE HARD TO STARTS

  • Transmission not in neutral.
  • Drive engaged.
  • Loose wires or connectors.
  • Dirt or water in fuel system.
  • Clogged fuel lines.
  • Choke cable malfunctioning.
  • Throttle cable malfunctioning.
  • Spark plug(s) malfunctioning.
  • Carburetor not adjusted properly.
  • Valve to tappet clearance set incorrectly.
  • Low engine compression.

ENGINE WILL NOT CRANK

  • Transmission not in neutral/drive engaged.
  • Battery low or discharged, or not properly connected.
  • Safety interlock switch engaged, not connected properly or malfunctioning.
  • Loose or faulty wires or connectors.
  • Ignition switch not connected properly or malfunctioning.
  • Starter not connected properly or malfunctioning.
  • Starter solenoid not connected properly or malfunctioning.
  • Seized internal engine components.

ENGINE RUNS BUT MISSES

  • Dirt or water in fuel system.
  • Spark plug(s) leads loose.
  • Spark plug(s) not properly gapped.
  • Loose wires or connections that intermittently short kill terminal of ignition module to ground.
  • Carburetor improperly adjusted.
  • Engine overheating.
  • Valve to tappet clearance set incorrectly.
  • Ignition module malfunctioning.

ENGINE WON’T IDLE

  • Stale fuel.
  • Carburetor gummed up.
  • Carburetor idle speed adjusting screw not set properly.
  • Dirt or water in fuel system.
  • Carburetor fuel idle adjusting screw not set properly.
  • Fuel tank vent plugged.
  • Spark plug(s) malfunctioning.
  • Valve to tappet clearance set incorrectly.
  • Low engine compression.

ENGINE OVERHEATS

  • Grass screen clogged.
  • Cooling fins clogged.
  • Shrouding clogged.
  • Excessive engine load.
  • Oil level too low.
  • Oil level too high.
  • Carburetor improperly adjusted.

ENGINE LOSES POWER

  • Oil level too low.
  • Oil level too high.
  • Air Filter clogged or plugged.
  • Dirt or water in the fuel system.
  • Excessive engine load.
  • Engine overheating.
  • Spark plug(s) malfunctioning.
  • Carburetor improperly adjusted.
  • Low engine compression.

ENGINE KNOCKS

  • Oil level is too low.
  • Oil level is too high.
  • Wrong type of oil.
  • Wrong type of fuel.
  • Internal engine components worn or damaged.

ENGINE USES EXCESSIVE AMOUNTS OF OIL

  • Wrong type of oil.
  • Wrong oil viscosity.
  • Clogged air breather assembly.
  • Air breather assembly not assembled correctly.
  • Worn or broken piston rings.
  • Worn cylinder bore.
  • Worn valve stems.
  • Worn valve guides
  • Engine crankcase overfilled with oil.

ENGINE BACKFIRES

  • Water in the fuel.
  • Fuel level low.
  • Bad fuse.
  • Kill switch malfunctioning.
  • Safety switch malfunctioning.
  • Wrong fuel mixture.
  • Worn valves.
  • Choke or throttle not set correctly.
  • Carburetor dirty.

Shop Small Engine Parts

If you come across anything we’ve forgotten please let us know.  We may be small engine experts but we also drink a lot.

– Jack

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Jack Hayes

Jack Hayes

Jack Hayes is the Head of Internet Marketing at LawnMowerPros and the editor of this blog. You can often find him creating featured articles, DIY guides, custom graphics and much more.