1. Troubleshooting Small Engine Systems Jason Spurlin 4/10/02 Virginia Tech Edited by the CTAE Resource Network February 2011

2. Troubleshooting Engine Systems PERFORMANCE OBJECTIVE On 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.

3. Ignition System Engine won’t Start CauseRemedy 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

4. Ignition System cont. Engine Lacks Power Magneto improperly timedreset air gap Engine Runs Unevenly Intermittent spark at plugcheck switches, check magneto for loose or damaged wires Other ignition problems: rust on iron plates faulty magnets

5. Armature air gap too large Disconnected spark plug wire Burned plug

6. Lubrication System

7. 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

8. 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

9. Broken air fin Clogged air passages

10. Fuel System

11. Engine Fails to Start CauseRemedy 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.

12. 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

13. Clean Air Filter Intact Primer Bulb Fuel Line Clean Carburetor

14. Compression System

15. 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

16. Missing head gasket Burnt valve Chipped piston

17. 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

18. Other Ailments Clogged exhaust system – Insects frequently build nests in exhaust pipes Associated equipment malfunctioning

19. Summary 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.

20. 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.