4-CYCLE OVERHEAD VALVE ENGINES - Small Engine Discount

TESTING
ENGINE KNOCKS
1. Check the blade hub, blade adapter, or crankshaft coupler for loose fit, loose bolts, or crankshaft key
damage. Remove, inspect, replace if necessary. Reinstall and re-torque the bolts to the proper torque.
2. Check the flywheel key and the flywheel and crankshaft keyway for wear or partial shearing. Replace
if any damage is evident. Tighten the flywheel nut to the proper torque.
3. Check for the correct ignition module air gap.
4. Remove the cylinder head and check for excessive carbon in the combustion chamber. Also check that
the head gasket fit is correct, and the spark plug for proper reach and heat range (correct spark plug for
the engine).
5. Check for the proper valve lash using a feeler gauge.
6. Check the internal components (piston, cylinder, connecting rod, crankshaft journal) for excessive
clearance. See Chapter 10 under "Specifications".
ENGINE OVERHEATS
1. Make sure the engine is not being overloaded. Remove excess load (sharpen blades, limit operation
speed, process less material).
2. Check the oil level and viscosity. Add or replace as necessary.
3. Check for clogged cooling fins or obstructions to the air flow. Remove the blower housing, clean and
reinstall.
4. Check the carburetor for correct adjustment or remove and clean the carburetor using tag wire and
compressed air. See Chapter 3 under "Service."
5. Check the engine R.P.M. setting using a vibratach or other tachometer and compare it to the R.P.M.
settings found on microfiche card #30 according to the engine model and specification number. Adjust
as necessary.
6. Check the ignition timing. See Chapter 8 "Ignition - Service."
7. Remove the cylinder head to check for excessive carbon buildup or a leaking head gasket. Clean or
replace as necessary.
SURGES or RUNS UNEVENLY
1. Check the fuel cap to make sure it is venting. Loosen the cap and retry engine operation.
2. Replace or clean the air filter.
3. Check the carburetor adjustment or clean the carburetor. See Chapter 3 under "Service."
4. Check the engine R.P.M. setting using a vibratach or other tachometer and compare it to the R.P.M.
settings found on microfiche card # 30 according to the engine model and specification number. Adjust
as necessary.
5. Visually check all linkages. Check the governor shaft, throttle shaft, or pivot points for binding.
6. Check the ignition module operation using a gap type tester installed between the high tension lead
and spark plug. Check for intermittent spark.
ENGINE MISFIRES
1. Check the spark plug for the proper application or a fouled condition. Replace if questionable.
2. Reset the carburetor following the adjustment procedure or clean the carburetor. See Chapter 3 under
"Service."
3. Check the ignition timing. See Chapter 8 under "Service."
4. Check for carbon buildup in the combustion chamber.
5. Check valve lash. Inspect the valves and valve seats for leakage. Check for scoring or discoloration on
the valve stem in the valve guide area. Recut the valves and seats if questionable. See "Valve Service"
in this chapter.
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