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Troubleshooting Small Engines by Jason Spurlin 4/10/02 Virginia Tech This presentation has not been edited by the Georgi PowerPoint Presentation
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Troubleshooting Small Engines by Jason Spurlin 4/10/02 Virginia Tech This presentation has not been edited by the Georgia Curriculum Office. Interest Approach. Bring in a push mower that will not crank and have students try to crank it.

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Troubleshooting Small EnginesbyJason Spurlin4/10/02Virginia TechThis presentation has not been edited by the Georgia Curriculum Office.

interest approach
Interest Approach
  • Bring in a push mower that will not crank and have students try to crank it.
  • Ask the students if they have ever experienced this frustration at home and if they were able to fix the problem.
  • Tell students that we are are going to spend time identifying and fixing problems for the next few days.
systematic troubleshooting
Systematic Troubleshooting


On a unit test, describe systematic troubleshooting on small engines with at least 70% accuracy.


  • Explain the principles of systematic troubleshooting.
  • Identify the fundamental operating requirements of small engines.
  • Use service manuals and troubleshooting guides to locate tolerances, clearances, and specifications.
systematic troubleshooting4
Systematic Troubleshooting
  • System of testing one component after another until the problem is located and repaired.

1. Look for the easiest things first.

2. Verify the five fundamental operating requirements.

3. Write down what you have done

fundamental operating requirements
Fundamental Operating Requirements
  • Proper Carburetion – correct proportion of clean, fresh fuel has to mix with combustion air
  • Correctly operating ignition system – strong ignition spark must be timed properly
  • Adequate Lubrication – correct amount of clean oil must coat engine components
  • Sufficient cooling – air that reaches engine should be less than 20oF hotter than ambient air.
  • Proper compression – at least 30-45 psi for starting and 90 psi during operation
check easiest things first
Check Easiest Things First
  • Is there clean, fresh fuel in the tank?
    • Fuel shouldn’t be more than 1 month old
  • Is the spark plug wire connected?
  • Is the oil level correct?
  • Gather pertinent information from the owner.
    • How was the engine acting before it stalled?
    • Did it start back? If so, how long before it did?
    • Did you hit an obstruction during operation?
eliminate operating requirements listen to the engine
Eliminate Operating Requirements(Listen to the Engine)


  • Try to start the engine.
    • If the engine spins but won’t start, eliminate lubrication.
    • While spinning the engine, check for sufficient compression. If sufficient, eliminate compression.
    • If engine stalls but doesn’t restart after it cools, eliminate cooling system.
    • Now you can focus on carburetion and ignition.
  • Once you have eliminated as many systems as possible, refer to a troubleshooting guides and service manuals to pinpoint and solve the problem.
troubleshooting guides
Troubleshooting Guides
  • Tables that have common problems, causes, and remedies listed in an easy to read format
  • Example information in a troubleshooting guide:
service manuals
Service Manuals
  • Service manuals are engine specific
  • Include service procedures and most common problems
  • Show exploded views of components that help during reassembly
  • Provide charts that list proper tolerances, clearances, and specifications
  • Troubleshooting is a process of elimination
  • Check easiest things first.
    • Is fuel in tank?
    • Is spark plug wire connected
    • Ask owner how the engine is performing
  • Verify the 5 fundamental operating requirements: carburetion, ignition, lubrication, cooling, compression.
  • Use troubleshooting guides to locate problem.
  • Use service manuals to locate tolerances, clearances, and specifications.
  • Write everything down that you check.
troubleshooting engine systems
Troubleshooting Engine Systems


On a lab project, perform systematic troubleshooting of the electrical, lubrication, cooling, fuel, and compression systems with at least 70% accuracy.


  • Identify symptoms of malfunctioning system components.
  • Inspect spark plug, flywheel key, and magneto.
  • Inspect and repair components of lubricating system.
  • Inspect, clean, and repair cooling fins, flywheel, and air shroud.
  • Inspect fuel tank, fuel pump, carburetor, reed valves (in two-cycles), fuel lines, filters, and air cleaner.
  • Inspect governor and adjust if necessary.
  • Identify and repair causes of poor compression.
ignition cont
Ignition cont.
  • Other ignition problems:
  • rust on iron plates
  • faulty magnets

Armature air gap too large

Disconnected spark plug wire

Burned plug

lubrication system18
Lubrication System
  • Lack of Lubrication Causes:
    • Engine to miss under load
    • Lack of power
    • Overheating
  • Engine uses excessive oil
    • oil level too high
    • oil filler cap loose of gasket damaged > replace gasket
    • oil passages obstructed > clean oil passages

Fill crankcase to proper level and/or check oil slinger

Drain oil to proper level

cooling system
Cooling System
  • A malfunctioning cooling system will cause the engine to overheat
  • When checking cooling system look for:
    • obstructed air flow
    • clogged cooling fins
    • broken cooling fins
    • broken flywheel vanes
    • damaged or removed shroud
    • low oil level

Broken air fin

Clogged air passages

fuel system22
Fuel System

Fuel system has to deliver clean, fresh, and properly proportioned fuel/air mixture to combustion chamber.


Intact Primer Bulb

Clean Air Filter

Clean Carburetor

Fuel Line


Most new carburetors do not have needle valves and cannot be adjusted, but many old types are still in operation.

compression system27
Compression System
  • The following are symptoms of poor compression.
    • Engine will not start
    • Engine knocks
    • Engine misses under load
    • Engine lacks power
    • Engine uses excessive oil
  • Common causes of poor compression.
    • Damaged or removed crankcase gaskets
    • Carbon deposits in combustion chamber
    • Weak valve springs
    • Leaking valves
    • Cracked porcelain on spark plug
    • Excessive cylinder and piston wear

Burnt valve

Chipped piston

Missing head gasket

checking compression
Checking Compression
  • An engine with proper compression will have a degree of resistance when the operator pulls on the starter rope
  • Use a compression tester
    • 30-45 psi min. for starting
    • 90 psi min. for efficient operation
other ailments
Other Ailments
  • Clogged exhaust system
    • Insects frequently build nests in exhaust pipes
  • Associated equipment malfunctioning
  • Once you have checked the easy things, work through the each system until you find the problem
  • Faulty ignition systems can be eliminated if there is spark at the plug. If not, focus attention on magneto, connecting wires, plug, and the flywheel magnets.
  • A faulty cooling system will cause the engine to overheat and stall, but cooling problems can be easily alleviated by making sure air passages and cooling fins are clean and intact.
summary cont
Summary cont.
  • The fuel system has to allow a CLEAN, proper fuel/air mixture to reach the combustion chamber. Make sure that fuel lines and filters are clear and that the carburetor is adjusted properly.
  • Poor compression is easily identified by resistance when rope starting and by using a compression tester. Problems are generally associated with leaky gaskets, leaking valves, and excessive cylinder wear.
  • Clogged exhaust systems also prohibit an engine from running properly.
  • REMEMBER: Check off each thing that you have checked and/or repaired.