Troubleshooting Small Engine Troubleshooting Small Engine SystemsSystems

Jason SpurlinJason Spurlin4/10/024/10/02

Virginia TechVirginia TechEdited by the CTAE Resource Network February 2011Edited by the CTAE Resource Network February 2011

Troubleshooting Engine SystemsTroubleshooting Engine Systems

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

ENABLING OBJECTIVES 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 SystemIgnition SystemEngine won’t Start

Cause Remedy

Disconnected spark plug wire

No spark at plug

Spark plug porcelain cracked

Spark plug fouled

Faulty magneto

Sheered flywheel key

Connect wire

check switches and magneto

replace plug

clean and regap

check air gap, if necessary overhaul mag.

replace flywheel key

Engine Misses under Load

Fouled Plug

Porcelain cracked

Improper spark plug gap

Pitted breaker points

Faulty condensor

clean and regap

replace plug

regap

replace points

check on a tester, replace if necessary

Ignition System cont.Ignition System cont.

Engine Lacks Power

Magneto improperly timed reset air gap

Engine Runs Unevenly

Intermittent spark at plug check switches, check magneto for loose or damaged wires

Other ignition problems:

• rust on iron plates

• faulty magnets

Armature air gap too large

Disconnected spark plug wire

Burned plug

Lubrication SystemLubrication System

Lubrication SystemLubrication 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 SystemCooling 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 SystemFuel System

Fuel SystemFuel System

Engine Fails to Start

Cause Remedy

No fuel in tank

Shut-off valve closed

Obstructed fuel line

Tank cap vent obstructed

Water in fuel

Overchoked

Improper carburetor adjustment

Primer bulb busted

Fill tank

Open valve

Remove and clean fuel line

Open vent

Drain tank and refill with clean fuel

Close shut off valve and pull cord until engine starts

Adjust carburetor

Replace primer bulb

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

Fuel System cont.Fuel System cont.Engine Misses Under Load

Improper carburetor adjustment

Reed valves stuck

Adjust carburetor

Clean or replace reed

Engine Lacks Power

Choke partially closed

Improper carburetor adjustment

Air cleaner dirty

Reed fouled (2 cycle)

Improper fuel/oil mixture (2 cycle)

Open choke

Adjust carburetor

Clean or replace air filter

Clean or replace

Drain tank; fill with proper mixture

Engine Surges or Runs Unevenly

Fuel tank cap vent hole clogged

Governor parts sticking or binding

Carburetor throttle linkage or throttle shaft binding or sticking

Improper carburetor adjustment

Dirty Carburetor

Open vent hole

Clean and repair if necessary

Clean, lubricate, or adjust linkage

Adjust carb

Clean carburetor

Clean Air Filter

Intact Primer Bulb

Fuel Line

Clean Carburetor

Compression SystemCompression System

Compression SystemCompression 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

Missing head gasket

Burnt valve

Chipped piston

Checking CompressionChecking 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 AilmentsOther Ailments

Clogged exhaust system– Insects frequently build nests in

exhaust pipes

Associated equipment malfunctioning

SummarySummary Once you have checked the easy things, work through

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.