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Do It Yourself - Outdoor Power Equipment Repair & Maintenance

Small Engine Troubleshooting

Small Engine Troubleshooting Posted in Small Engines

Your Engine just started acting up and you don't know what to do.

Below is a chart of common Engine problems and some easy troubleshooting to fix the problem you may be experiencing.

This chart is to be used as a guideline for troubleshooting engine problems. For specific engine tuning or recommendations consult your owner's manual.

  • Engine Will Not Crank[GO]
  • Cranks - Will Not Start[GO]
  • Runs Rough On Low & Will Not Accelerate[GO]
  • Backfires on Full Throttle[GO]
  • Electrical system problem[GO]
  • Engine not running (After Hot Test)[GO]
  • Stops on High Idle[GO]
  • Hot - Will Not Restart[GO]
  • Cannot Reach High Idle RPM (No Load)[GO]
  • Starting Hints - Command Retractable Start Engine[GO]

ENGINE WILL NOT CRANK
  • Battery lead connections are loose.
  • Battery charge low or discharged.
  • Battery amperage too low.
  • Starting leads reversed.
  • Fuse in wiring harness blown.
  • Keyswitch wired wrong.
  • Safety switch malfunctioning.
  • Wiring harness incorrect.
  • Wiring harness wired wrong.
  • Starting cable connectors loose.
  • Connectors corroded or worn.
  • Starter/Solenoid malfunctioning.
  • Electric clutch air gap wrong.
  • Drive pulley against engine PTO face.
  • Drive belt wedged between idler pulley.
  • Drive belt wedged between belt guide.
  • Drive belt tension adjusted too tight.
  • Starting torque too high for starter.
  • Automatic compression release inoperative.
  • Combustion chamber flooded with oil/gas.
  • No oil in crankcase causing seized rod.
  • Drive shaft coupling forcing engine shaft against internal thrust face eliminating crankshaft end play.
  • Transmission brakes too tight.
[TOP]
CRANKS - WILL NOT START
  • Fuel tank empty.
  • Fuel hose kinked, pinched.
  • Fuel filter clogged.
  • Fuel valve shut off
  • Fuel solenoid inoperative.
  • LPG Regulator not opening.
  • Water in fuel, stale fuel.
  • Wrong type fuel (Diesel).
  • Throttle control in stop position.
  • Choke not fully closed.
  • Choke on, flooding hot engine.
  • Power take off clutch on.
  • Safety interlocks inoperative.
  • Spark plug wire disconnected.
  • Spark plug improperly gapped.
  • Wrong type of spark plug.
  • Wiring harness not connected.
  • Wiring broken, loose or wrong.
  • Transmission not in neutral.
  • Electrical clutch not adjusted.
  • Cranking speed too slow to start.
  • Spark plug loose.
  • Low or no compression.
[TOP]
RUNS ROUGH ON LOW & WILL NOT ACCELERATE
  • Spark plug gap incorrect.
  • Engine not properly warmed up.
  • Running out of fuel.
  • Low idle set too low (Below 1000 RPM).
  • Low idle fuel setting too lean.
  • Electric clutch dragging.
  • Parasitic load on PTO shafts.
  • Crankshaft end play zeroed drive.
[TOP]
BACKFIRES ON FULL THROTTLE
  • Water contaminated fuel.
  • Running out of fuel.
  • Fuel mixture too rich or too lean.
  • Carburetor fuel solenoid shorting.
  • Throttle or choke improperly set.
  • Dirty carburetor needs cleaning.
  • Kill switch contacting intermittently.
  • Keyswitch malfunctioning.
  • Safety interlock(s) malfunctioning.
  • Faulty fuse in unit control box.
  • Leaking, worn valves in engines.
[TOP]
ELECTRIC SYSTEM PROBLEMS
Charges and gradual discharges
  • Improper ground causing battery to lose charge when accessories activated.
  • Faulty battery will not hold charge.
Will not charge
  • Regulator-Rectifier failed.
  • Regulator-Rectifier not grounded.
  • Flywheel magnet not charged.
  • Fuse blown or circuit breaker open.
Blowing fuses
  • Regulator-Rectifier burned out.
  • Leads pinched causing shorting.
  • Alternator stator shorted.
Electric clutch will not engage
  • Wrong Regulator-Rectifier used.
  • Wiring wrong or not grounded.
Engine runs on when switched off
  • Ignition grounding terminal or ground lead not connected at ignition module.
  • Faulty switch.
[TOP]
ENGINE NOT RUNNING (AFTER HOT TEST)
Smoke rises out of top of horizontal shaft engine or flywheel screen on vertical shaft engine.
  • Paint or oil burn off.
  • Battery cables reversed causing charging stator to short out.
  • Defective regulator-rectifier causing charging stator to short out.
  • Electric clutch - No running clearance.
[TOP]
STOPS ON HIGH IDLE
  • Running out of fuel.
  • Running out of oil in crankcase.
  • Carburetor solenoid malfunctioning.
  • Keyswitch malfunctioning.
  • Safety interlocks malfunctioning.
  • Spark plug lead loose.
  • Fuse blown in control box.
  • Carburetor out of adjustment.
  • LPG Regulator malfunctioning.
  • Loss of vacuum to LPG Regulator.
  • Tight drive belt causing crankshaft bearing to seize.
[TOP]
HOT - WILL NOT RESTART
  • Overheated - Clogged in cooling fins.
  • Overheated - Blocked shrouding.
  • Closed choke flooding engine.
  • Throttle not in midway position.
  • Throttle left in stop position.
  • Carburetor solenoid malfunctioning.
  • Fouled spark plug.
  • Kill lead shoring out.
  • Ran out of fuel.
  • Lost compression.
  • LPG Regulator not functioning.
  • Vacuum too low to open LPG Regulator.
[TOP]
CANNOT REACH HIGH IDLE RPM (NO LOAD)
  • Choke not completely opened.
  • Throttle control cable clip loose.
  • Throttle control improperly installed.
  • Fuel filter or line clogged.
  • Fuel inlet line too small.
  • Fuel running low.
  • Fuel tank too far from engine.
  • Fuel pump malfunctioning.
  • Gravity feed tank below carburetor.
  • Foreign material in carburetor.
  • Carburetor out of adjustment.
  • Spark plug gapped wrong causing intermittent firing.
  • Drive system binding.
[TOP]
STARTING HINTS - COMMAND RETRACTABLE START ENGINE
Dual control cable instructions
  1. Close choke.
  2. Set throttle to full.
  3. Pull starter rope to set engine on compression.
  4. Return starter rope, then give a full, steady pull.
  5. When engine starts, return choke to full open immediately.
  6. Position throttle control to desired setting..
Single control cable instructions
  1. Move throttle/choke lever to choke position.
  2. Pull starter rope to set engine on compression.
  3. Return starter rope, then give a full, steady pull.
  4. When engine starts, move the control lever to the desired setting.


Jack's Safety Tips: Before servicing or repairing any power equipment, disconnect the spark plug and battery cables. Remember to wear appropriate safety glasses and gloves to protect against harmful chemicals and debris. View our Disclaimer.