Small Engines Small Engine Troubleshooting

Published on March 20th, 2015 | by Jacks


Small Engine Troubleshooting

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

  • 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.

  • 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.


  • 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.


  • 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.


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.


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.


  • 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.


  • 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.


  • 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.


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.

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About the Author

Jack's Small Engines has been providing parts for outdoor power equipment online since 1997. We also run a service center for outdoor power equipment like riding mowers, snow blowers, generators, chainsaws, and just about anything else.

24 Responses to Small Engine Troubleshooting

  1. Jack Sminkey says:

    Honda small engine 161 cm ( Power washer.) Engine GJAEA 3584766 N5AF.. No spark when trying to start.. The on and off switch is okay. magneto is in Question? No points or condenser. What could it be?
    Thank you, Jack Sminkey

  2. david canup says:

    I have a 3.5 hp tecumseh engine on a sears edger and I can not get it to start I am not getting a spark at the plug.
    I replaced the coil and cleaned the fly wheel and replaced the coil. it does not have points or a condenser. I cleaned the flywheel I check the stop switch by disconnected the stop wire I can holt the spark plug wire and I feel nothing.What could I be missing.

  3. bill pitt says:

    i cant get motor to idle its a b&s 300 series 4.50 model 9t602 type 5019 serial 11082954 aug 2011 I clean the carb ,replaced diapharm ,checked for water ,cleaned valves replaced head gasket ,checked flywheel key, checked breather tube and o-ring.I ran out of ideal’s any help would be appricated

  4. richard says:

    morning my name is Richard from Australia and have just gained a contract (I am a motor mechanic} to maintain a fleet of vehicles and also trailer winches with kohler command pro 14 429cc engines and am not up to speed on small engines except basics. I wonder if you can help me , engine is not charging battery (only putting 12.6v into battery) how does battery get charged and what could problem be and how to rectify it . other problem is key start wont turn motor over but I am assuming its because of battery low . any help would be much appreciated thanks Richard.

  5. DanD says:

    I have a 3.5 hp Tecumseh engine on a sears edger and I can not get it to start I am not getting a spark at the plug.
    I’ve check the stop switch by disconnected the stop wire.
    I can hold the spark plug wire and I feel nothing.
    I’ve spun the crank with a drill motor, plug on a tester, no spark.

  6. Steve Szabo says:

    I have four cycle tecumaseh Engine 8 hp Rear engine Rider Toro. Electric Start. Key start wont tur..
    Help would be appricateg.

    Steve Szabo

  7. Al Schrader says:

    To Jack Sminkey or anyone with this problem.
    Sometimes the new coil is defective. You can test a coil with an ohm meter.
    Be sure your coil ground wire has a solid corrosion free connection and make sure your kill wire is not shorted to ground.
    You can test these circuits with your ohm meter.
    And lastly make sure the magnet is strong and the magneto gap is correct.
    You can test the strength of the magnet by bringing a piece of steel sheet metal close and the magnet should grab it out of your hand.

    Some B&S models have points and some don’t. If your is a points model check the points for burned contacts and the proper gap.
    test instruments are your best investment verses replacing this or that until you find what was bad.
    Good luck.

  8. Frank Paine Jr says:

    I’m trying to tune up my DR mower- it has a 15 horse twin v Kawasaki engine- I replaced the plugs and both coils, but still no spark to the plug…not sure why.Its getting gas, but no spark. Help me!

  9. Robert Derry says:

    i have a 17 hp kohler command that backfires when i try to start it, it has a new coil and i checked the valves what else could i check?

  10. Al says:

    I have a Honda self propelled lawn mower that will not stop right away when the throttle is moved to the stop position when I get finished mowing my lawn. It seems to “Diesel”. What do I need to do to correct this problem.


  11. Paul says:

    Fairly new honda engine on waterpump.
    Crank locks up when pulling recoil.
    Will free uo by forcing propeller back .
    Then back to lock up when recoil is pulled.
    Sounds like something loose inside block.
    Engine was running fine before last shut off.
    Had to get water out of fuel tank. Engine was turned upside down
    to drain fuel.

  12. Ed Akerley says:

    Kohler CH25 (25hp). Soon after starting motor the crankcase breather tube begins flooding into the carburator, gas eventually begins mixing with motor oil in the crankcase and motor floods itself out. Replacement with a new carburator didn’t work.

  13. Marc says:

    Have a 140CC Honda pressure washer engine that goes max RPM for some unknown reason so I replaced it with a spare Tecumseh I had laying around. I thought maybe the engine was undersized for the application and getting overheated then losing it’s regulatory mind.

    Adapted the Honda to a lawn mower, It still works good for a while then goes RPM bonkers.

  14. Ken Dill says:

    Have a Husqvarna weed eater that runs great until it gets warmed up.It will cut off and can not get fire to the plug until it cools off. Could this be the coil breaking down and how bad is it to change. Thanks, Ken Dill

  15. Shaun Keen says:

    July 13, 2015 at 10:16 am
    hi, I have a Stihl ts400 cut off saw and when I pull the starter cord there’s hardly anything there, it is so easy to pull so fails the compression test of holding the cord and saw staying still and not falling to the ground. I have looked and looked for answers but I can’t find any help at all, so I’m hoping u maybe be able to give me some advice. I am thinking it needs a new pot, piston and maybe cylinder head but I’m unsure if it will need a new crank and bearings also. I have never got that far with repairs but I am getting better I just need that helping hand on a couple of things. So if u can give me some advice as to why there is no power when u pull the pull cord I will be gladly appreciated mate, and thanks buddy

  16. gordie clark says:

    i have a husky 17.5 hp I put a new battery in and when I turn the key I get nothing,was running fine now nothing please help thank you.

  17. GUY says:


  18. Pingback: How 4 Stroke Engines Work

  19. joe reed says:

    having trouble with a john deere 420 burning up clutches bought a new one have a guy adjust it for me ran for a bit and smoke new clutch what is going on here?

  20. Victor Matos says:

    MY old Bolens starts right up but as soon as you release the key after start up it shuts down. Help, I’ve never seen this problem.

  21. J knight says:

    I purchased a jdz445 w 25 hp Kawasaki. Replaced carb. Noted oil in exhaust shield. Did not try to start. Drained crankcase. Oil consistency & color is like coca cola. Smells a bit of raw fuel. Any comments – is there potential source ofbfuel leakage into crankcase for this engine?

  22. ROB says:

    well, if a snow blower motor is backfiring in the muffler it could be the crab to lean on gas mixture our plunged up needs cleaning blowing out with compressor check float level, could be the pin in the fly wheel is on it’s ends puts the motor out of time change the fly wheel pin if it’s not the crab valves should be set at 001 our 002 like a tight snug fit on your feeler gauge this is a tecumseh engine 12 hp same for the 11hp

  23. ROB says:

    hi, if any one having trouble with lawn mowers our snow blowers cranking just back firing if it starts wont run long back firing pulling the pull cord out of your hand this is defiantly the fly wheel pin is cut in half our well on the way take off your fly wheel and replace the half moon pin

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