Trouble Shooting

Rev - Nov 29, 2017

By Jan Zumwalt (EAA #66327)


T rouble shooting is problem solving with the intended goal of finding and repairing a failed product, process, or system. It should be a logical, systematic search for the failure. It is desirable to accomplish the task in the least amount of time while needing the fewest resources and manpower.

Remember: All equipment has a purpose, function, or goal, and each component is always designed to have input and output. Trouble shooting can be divided between what is upstream or downstream of a component.

  1. If possible, get documentation that gives the relationship of components and gives input/output expectations. You can not troubleshoot a piece of equipment unless you have expectations of what the input and output should be.
  2. Assume only one component or system is bad. Except in the case of catastrophic failure i.e. fire, impact, power surge, or water damage, it is extremely rare to have multiple component failures.
  3. If all inputs to a system are good and one or more outputs is bad, then this component or system is bad.
  4. Start with the most common or easiest system or component. Try to divide and subdivide the systems until the problem is found.

There is nothing more frustrating than an engine that develops problems giving a sense of insecurity or loss of dependability. This guide is presented to quickly identify the cause of engine problems.

Note: The solutions given are in the approximate order that testing or checking should be performed. However, there is no substitute for common sense and an understanding of the engines history.


As soon as practical, an engine problem should be narrowed by the process of elimination into one of the three following systems...

 1) Mechanical
 2) Electrical
 3) Fuel

Mechanical problems often are associated with abnormal noise, compression, leaks, or oil consumption.

Electrical problems can be quickly assessed by checking for a spark, checking each exhaust pipe for heat, and checking the timing.

Fuel should be drained from sumps and filters then checked. The carb and spark plugs can be smelled. A small amount of fuel poured in the carb will verify whether the engine is wanting to start but is starved of fuel.


Table of Contents
01. Will Not Start
02. Low Power and Uneven Running
03. High Oil Temperature
04. High Oil Consumption
05. Low Oil Pressure
06. High Oil Pressure
07. Does Not Accelerate Properly
08. Bad Idle
09. Does Not Develop Full Power
10. Stops or Dies Unexpectedly
11. Vibrates Excessively
12. Throws Alternator Belt
13. Overheats
14. High Cylinder Head Temperature (CHT)
15. Won't Stop When Switch is Turned Off
16. Carburetor Leaks Fuel
17. Backfires or "Spits Back" in Carburetor
18. Misses Intermittently
19. Misses Regularly
20. Scattering Misfire
21. Single Cylinder Miss at High Speed
22. Single Cylinder Miss at Low Speed
23. Pre-Ignition
24. Excessive Carbon Deposit
25. Magneto - No Spark
26. Crankcase Fills with Oil (Dry-sump System)
27. Exhaust Flame Mixture Analysis
28. Mixture Too Rich
29. Mixture Too Lean Mixture



01 - Will Not Start
01. Lack of fuel
02. Ignition switch off
03. Under-priming or over-priming
04. Incorrect throttle setting
05. Cold oil
06. Defective battery (battery ignition systems)
07. Dirty or Defective spark plugs
09. Bad solenoid
10. Bad voltage regulator
11. Water in magneto
12. Wet ignition harness
13. Wrong type or grade of fuel
14. Spark advance retarded too far
15. Vapor in fuel system
16. Water in carburetor
17. Defective ignition wiring
18. Booster magneto Defective
19. Incorrect valve and/or ignition timing
20. Defective magneto
21. Broken impulse coupling
22. Magneto breaker points Defective
23. Incorrect valve clearance
24. Defective priming system
25. Internal trouble in carburetor
26. Intake manifold air leaks
27. Broken, shredded or Defective camshaft
28. Internal engine failure
29. Spark plug wires crossed
30. Miscellaneous (unusual condition, sound or low compression)



02 - Low Power and Uneven Running
01. Mixture too rich or too lean
02. Induction leaks
03. Defective or fouled spark plugs and loose plug connections
04. Improper fuel grades
05. Wet or Defective ignition wiring
06. Engine overheating
07. Defective magneto breaker points
08. Defective or dirty magneto carbon brushes
09. Improper valve and/or ignition timing
10. Propeller out of track, or hub nut loose
11. Carburetor heat control malfunction
12. Cracked engine mount or loose mount bolts
13. Foreign matter in induction system or fuel lines
14. Incorrectly adjusted carburetor control linkage
15. Fuel selector leaking or Defective
16. Warped or burned valves or valve seats
17. Broken valve springs
18. Defective or sticking pistons or cylinders
19. Cracked pistons or cylinders
20. Bent pushrods
21. Defective Cylinder or Head gaskets
22. Magneto ground wire loose and grounding
23. Carburetor icing
24. Improper fuel pressure
25. Defective rocker arms or bearings
26. Defective valve guides
27. Bent crankshaft
28. Crosswind on propeller during ground operation
29. Spark plug wires crossed



03 - High Oil Temperature
01. Low oil supply
02. Defective oil temperature gauge
03. Airflow through oil cooler blocked
04. Oil cooler bypass valve malfunction
05. Cylinder baffles missing or insecure
06. Poor airflow around oil tank
07. Clogged oil lines or screens
08. Overheated bearings
09. Dirty or improper grade of oil
10. Improper grade of fuel
11. Improper ignition timing
12. Main bearing shifting in crankcase bearing bore.



04 - High Oil Consumption
01. Thin oil or wrong grade
02. Improper venting of oil system
03. Piston rings worn, broken or incorrectly installed
04. Breather line exiting in low pressure area and blocked or
05. Oil level too high, over filling
06. Missing vacuum break hole on breather line
07. Cracked pistons
08. Defective supercharger seal
09. Piston oil drain holes clogged
10. Oil pressure too high
11. Too much clearance between intake valve and guide
12. Scored cylinder walls
13. Excessive piston clearance
14. Excessive bearing clearance
15. Faulty scavenger pump



05 - Low Oil Pressure
01. Low oil supply
02. Oil pump not primed
03. Improper setting of pressure relief valve
04. Foreign matter in relief valve
05. Defective pressure gauge, or clogged gauge line
06. Improper grade of oil
07. High oil temperature
08. Leak in suction lines
09. Dirt in oil screens
10. Foaming in oil tank
11. Oil congealed in intake line
12. Excessively diluted oil
13. Broken oil line
14. Excessive cam follower to crankcase clearance
15. Excessive bearing clearance or wrong undersized bearings
16. Crankshaft plugs leaking or missing
17. Worn oil pump gears
18. Broken oil pump gears or drive shaft



06 - High Oil Pressure
01. Improper grade of oil
02. Pressure relief valve stuck closed or improperly adjusted
03. Oil cold or frozen
04. Oil pipe bent or crushed
05. Defective pressure gauge
06. Low bearing clearance
07. Oil Screen or filter clogged
08. Bearing tight due to engine overheating



07 - Bad Engine Acceleration
01. Incorrectly adjusted carburetor
02. Defective accelerating pump
03. Cold oil
04. Defective tachometer
05. Improper propeller pitch or warped propeller
06. Improper throttle or mixture control linkage adjustment
07. Fuel valve leaking or not operating properly
08. Improper spark adjustment
09. Improper engine timing
10. Internal carburetor trouble, or pressure-type carburetor in gravity fuel system
11. Air leaks or restriction in induction system



08 - Poor Idle
01. Carburetor control linkage improperly adjusted
02. Loose spark plug connectors
03. Water or oil in magnetos
04. Burned or pitted contact breaker points
05. Improper magneto timing
06. Defective ignition harness
07. Improper grade of fuel
08. Incorrect idling speed adjustment
09. Throttle valve closing too far
10. Idling jet restricted
11. Air leaks in induction system
12. Vapor in fuel system
13. Improper fuel pressure
14. Internal carburetor trouble
15. Partial obstruction in fuel lines
16. Fuel valve leaking or not operating properly
17. Defective primer valve
18. Improper valve clearance
19. Low cylinder compression
20. Excessive play in carburetor control linkage



09 - Engine Does Not Develop Full Power
01. Carburetor control linkage improperly adjusted
02. Mixture too lean or too rich
03. Throttle valve not fully open
04. Improper grade of fuel
05. Air leak in carburetor
06. Incorrect fuel pressure
07. Improper valve clearance
08. Improper grade of oil
09. Oil too hot or too cold
10. Rocker arms not properly lubricated
11. Incorrect valve or ignition timing
12. Defective spark plugs
13. Weak magneto magnets
14. Burned or pitted contact breaker points
15. Excessive carbon and pre-ignition
16. Intake manifold too cold
17. Pressure type carburetor in gravity system
18. Weak or broken valve springs
19. Low cylinder compression
20. Valve seats scored or worn
21. Bent push rods
22. Excessive back pressure from exhaust manifold
23. Engine stiff or tight
24. Incorrect propeller setting, or warped propeller blades
25. Engine overheating
26. Carburetor venturi too small
27. Carburetor icing
28. Improper grade of fuel
29. Defective supercharger



10 - Engine Stops
01. Magnetos grounded
02. Out of fuel
03. Carburetor jets restricted
04. Air or vapor lock in fuel line
05. Fuel lines partially obstructed
06. Foreign object in induction system
07. Water in fuel
08. Broken fuel lines
09. Sheared timing gears
10. Internal structural failure
11. Propeller contacts solid object
12. Air vent or fuel tank obstructed



11 - Engine Vibrates Excessively
01. Propeller out of balance or out of track
02. Bent crankshaft
03. Unequal valve clearance
04. Defective spark plugs
05. Engine loose on mount
06. Propeller hub nut loose
07. Carburetor icing
08. Incorrect carburetor setting
09. Engine too cold
10. Improper ignition timing
11. Worn dynamic dampner bushings or pins



12 - Engine Continually Throws Alternator Belt
01. Bent pulley
02. Alternator bearings or armature
03. Worn dynamic dampener bushings or pins



13 - Engine Overheats
01. Retarded spark or spark timed late
02. Defective water circulation
03. Defective oil circulation
04. Thin oil
05. Lean Mixture
06. Camshaft out of time
07. Idling engine too long
08. Running air cooled engine on ground too long
09. Low oil cooling
10. Low oil supply
11. Running engine with radiator or cowling shutters closed
12. Excessive carbon
13. Engine improperly cowled
14. Overheated bearing
15. Tight bearings or pistons out of line



14 - High Cylinder Head Temperature (CHT)
01. Mixture too lean
02. Improper grade of fuel
03. Air leaks in induction system
04. High carburetor air inlet temperature
05. Magnetos improperly timed
06. Defective cylinder baffles, fins, or restrictions in airflow
07. Incorrect valve operation or clearance
08. Restrictions in exhaust system
09. Temperature gauge Defective
10. Thermocouple wires too close to exhaust manifold
11. Spark retarded
12. Pre-ignition through carbon or Defective spark plugs
13. Warped valves
14. Loose valve seats and guides
15. Worn valve guides



15 - Engine Won't Stop When Switch is Turned Off
01. Magneto ground wires loose or broken
02. Faulty magneto switch
03. Engine excessively hot
04. Incandescent carbon in cylinders



16 - Carburetor Leaks Fuel
01. Leaky or stuck float
02. Excessive fuel supply pressure
03. Poor seating of needle valve
04. Worn float fulcrum pin
05. Improper float level
06. Loose needle valve seat



17 - Engine "Spits Back" in Carburetor
01. Cold engine or cold mixture
02. Lean mixture
03. Air leaks in manifold
04. Air leaks around intake valve stems
05. Weak valve springs
06. Sticking valves
07. Spark plug wires crossed or incorrectly connected
08. Ignition out of time or retarded
09. Camshaft out of time
10. Overheating
11. Carbon
12. Improper grade of fuel
13. Water in gasoline



18 - Engine Misses Intermittently
01. Incorrect mixture
02. Improper grade of fuel
03. Water in fuel
04. Air leaks in induction system
05. Slow valve action
06. Defective magnetos or ignition harness
07. Distributor points or contact breaker points dirty or pitted
08. Carburetor air heater Defective
09. High oil temperature
10. Defective spark plugs
11. Improper timing
12. Carburetor icing
13. Magneto ground wire swinging and periodically grounding



19 - Engine Misses Regularly
01. Fouled spark plug
02. Defective spark plug
03. Broken or grounded spark plug wire
04. Improper valve clearance
05. Low compression on one or more cylinders
06. Defective magneto distributor head



20 - Scattering Misfire
01. Lean mixture
02. Rich mixture
03. Water in gasoline
04. Air leak in intake manifold
05. Intake valve holding open
06. Sticky valve guides
07. Weak valve springs
08. Excessive breaker point clearance
09. Weak breaker arm spring
10. Excessive rotor contact gap clearance
11. Moisture on distributor block
12. Faulty spark



21 - Single Cylinder Miss at High Speed
01. Shorted spark plugs
02. Shorted spark plug wire
03. Shorted distributor block
04. Spark plug gap too wide
05. Weak exhaust valve springs
06. Low valve tappet clearance



22 - Single Cylinder Miss at Low Speed
01. Shorted Spark Plug
02. Shorted Spark Plug Wire
03. Shorted Distributor Block
04. Wrong Spark Plug Gap
05. Weak Compression
06. Air Leak Around Intake Valve Stem
07. Weak Exhaust Valve Spring



23 - Causes of Pre-Ignition
01. Carbon on cylinder, piston, or head
02. Overheating
03. Excessively rich mixture
04. Ignition out of time
05. Spark plug wires crossed or connected to wrong cylinder



24 - Excessive Carbon Deposit
01. Engine flooded with oil
02. Worn piston rings
03. Inferior quality of engine oil
04. Rich mixture
05. Engine operated for long period without cleaning carbon



25 - No Spark
01. Breaker Point Clearance Incorrect
02. Breaker Points Burned or Dirty
03. Collector Brush Worn or Dirty
04. Distributor Brush Worn or Dirty
05. Distributor Segments/Rotor Contact Corroded or Burnt
06. Distributor Condenser Shorted or Punctured
07. Collector Ring Shorted or Dirty
08. Rotor Shorted or Dirty
09. Primary Winding Shorted or Dirty
10. Secondary Winding Shorted or Burned Out
11. Loose or Corroded Connection Within The Magneto
12. Ground Wire or Switch Shorted
13. Moisture Within The Magneto
14. Armature Touches Pole Pieces
15. Foreign Material Collected On Armature
16. Defective Spark Plugs
17. Carbon Tracks Resulting From Flashover (Moisture).
18. Magneto Magnets Weak or Crossed
19. Magneto E-Gap Incorrect
20. Magneto Primary Circuit Grounded or Open
21. Magneto Secondary Circuit Grounded or Open
22. Magneto Ground Wire or Switch Grounded
23. Magneto Condenser Circuit Open or Shorted, or Condenser Punctured



26 - Crankcase Fills with Oil (Dry-sump System)
01. Scavenger pump has lost its prime
02. Scavenger pump screen stopped up
03. Scavenger suction or pressure lines stopped up
04. Air leak in suction side of scavenger pump
05. Broken scavenger pump drive
06. Scavenger pump badly worn



27 - Exhaust Flame Mixture Analysis
01. Rich Mixture: Long deep blue flame with red tip, black smoke.
02. Lean Mixture: Short irregular light blue flame with yellow tip.
03. Proper Mixture: Quick blue flame without yellow tip.
04. Oil pumping is shown by blue or blue/grey exhaust smoke.



28 - Mixture Too Rich
01. High fuel pressure
02. Oil in cylinders
03. Carburetor float valve seating improperly
04. Float leaking air
05. Jet gaskets of improper thickness or out of shape
06. Float level too high (these troubles would be responsible for the carburetor flooding and a rich mixture, particularly at low speeds)



29 - Mixture Too Lean
01. Low fuel in tank
02. Partially clogged fuel line
03. Low air pressure in pressure fuel tank
04. Air vent on fuel tank clogged
05. Fuel filter or jets clogged
06. Carburetor float level too low
07. Water in carburetor or system
08. Air leaks in induction system
09. Sticking valves