Ultimate Magneto Troubleshooting Guide

Possible Cause:

Incorrect external timing to engine.

Remedy:

Consult engine manufacturer's specification for ignition timing. Correct as required.

Possible Cause:

Incorrect internal timing.

Remedy:

Consult Champion Aerospace Manual L-1363, Section 7.11 for internal timing specifications. Correct as required.

Possible Cause:

Point gap setting incorrect.

Remedy:

Consult Champion Aerospace Manual L-1363, Section 7.11 for point gap specifications. Correct as required.

Possible Cause:

Faulty impulse coupling

Remedy:

Consult Champion Aerospace Manual L-1363, Section 3.3.4, for impulse coupling specifications and inspection procedures.

Possible Cause:

Over-torqued impulse coupling nut

Remedy:

Torque nut to 120-320 in-lbs on magnetos with attached drive gears. There must be .010 to .020" play between drive gear and impulse coupling. Correct as necessary.

Possible Cause:

Worn pawls or stop pin

Remedy:

Inspect pawls and stop pin for wear. Correct as necessary.

Possible Cause:

Impulse coupling fails to return to unwound position

Remedy:

Inspect impulse coupling nut for torque.

Possible Cause:

Fouled spark plugs

Remedy:

Clean spark plugs according to manufacturer's specification.

Possible Cause:

Incorrect spark plug gap.

Remedy:

Re-gap spark plug to manufacturer's specifications.

Possible Cause:

Faulty ignition switch.

Remedy:

Inspect ignition switch for possibility of intermittent grounding and proper operation. Repair or replace as necessary.

Possible Cause:

Corrosion on harness lead contacts.

Remedy:

Consult manual L-1499 for proper cleaning and inspection procedures. Correct as required.

Possible Cause:

Broken rotor shaft at cam slot.

Remedy:

Consult Champion Aerospace Manual L-1363, Section 3.3.3.A.

Possible Cause:

Magneto Internal Component Failure:

Remedy:

Consult Champion Aerospace Manual L-1363, Section 3, for specifications and inspection procedures.

Possible Cause:

Points

Remedy:

Inspect for excessive burning, pitting, corrosion, gap setting and general operation. Replace as necessary.

Possible Cause:

Cam

Remedy:

Inspect cam for excessive wear or unevenness that could cause "point spread". Correct as necessary.

Possible Cause:

Condenser

Remedy:

Inspect for faulty P-lead connection, P-lead stud for over-torqued condition, damaged pigtail connector and damaged grounding. Replace as necessary.

Possible Cause:

Coil

Remedy:

Inspect for cracks, damage to high tension strap or pigtail connector and integrity of windings. Replace as necessary.

Possible Cause:

Distributor Gear

Remedy:

Inspect electrode finger for looseness, gear teeth, shaft. Inspect carbon brush for damage. Replace as necessary.

Possible Cause:

Distributor Block

Remedy:

Inspect distributor towers for evidence of abrasion or excessive burning. Examine rotor gear bushings for wear. Replace as necessary.

Possible Cause:

Incorrect or non-standard starting procedures.

Remedy:

Consult engine manufacturer's operation manual for proper operation and performance. Correct as required.

Possible Cause:

Faulty fuel delivery system.

Remedy:

Consult engine manufacturer's manual for specifications and operation. Correct as required.

Possible Cause:

Inoperative retard contact point circuit.

Remedy:

Inspect wiring connections and operation of points. Correct as required.

Possible Cause:

Impulse coupling not staying engaged while starter engaged.

Remedy:

Inspect impulse coupling for operation. Correct as required.

Possible Cause:

Inoperative retard contact point circuit.

Remedy:

Inspect for faulty wiring, timing, or inoperative contact points. Correct as required.

Possible Cause:

Non-impulse magneto not grounded while starter engaged.

Remedy:

Inspect and correct as required.

Possible Cause:

Broken rotor shaft at cam slot.

Remedy:

Consult Champion Aerospace Manual L-1363, Section 3.3.3.A.

Possible Cause:

Incorrect external timing to engine.

Remedy:

Consult engine manufacturer's manual for specifications of ignition timing. Correct as required.

Possible Cause:

Incorrect internal timing.

Remedy:

Consult Champion Aerospace Manual L-1363, Section 7.11, for internal timing specifications. Correct as required.

Possible Cause:

Fouled spark plugs.

Remedy:

Clean spark plugs according to manufacturer's specifications.

Possible Cause:

Incorrect spark plug gap.

Remedy:

Regap spark plug to manufacturer's specifications.

Possible Cause:

Faulty spark plug.

Remedy:

Test spark plug according to manufacturer's specifications.

Possible Cause:

Faulty ignition lead.

Remedy:

Consult Champion Aerospace Harness Maintenance Manual L-1499, for ignition lead troubleshooting information.

Possible Cause:

Faulty ignition switch.

Remedy:

Inspect ignition switch for possibility of intermittent grounding and proper operation. Repair of replace as necessary.

Possible Cause:

Magneto Internal Component Failure:

Remedy:

Consult Champion Aerospace Manual L-1363, Section 3, for specifications and inspection procedures.

Possible Cause:

Points

Remedy:

Inspect for excessive burning, pitting, corrosion, gap setting and general operation. Replace as necessary.

Possible Cause:

Cam

Remedy:

Inspect cam for excessive wear or unevenness that could cause "cam spread". Correct as necessary.

Possible Cause:

Condenser

Remedy:

Inspect for faulty P-Lead connection, P-lead stud for over-torqued condition, damaged pigtail connector and damaged grounding. Replace as necessary.

Possible Cause:

Coil

Remedy:

Inspect for cracks, damage to high tension strap or pigtail connector and integrity of windings. Replace as necessary.

Possible Cause:

Distributor Gear

Remedy:

Inspect electrode finger for looseness, gear teeth, shaft. Inspect carbon brush for damage. Replace as necessary.

Possible Cause:

Distributor Block

Remedy:

Inspect distributor towers for evidence of abrasion or excessive burning. Examine rotor gear bushings for wear. Replace as necessary.

Possible Cause:

Rotor shaft at cam slot

Remedy:

Consult Champion Aerospace Manual L-1363, Section 3.3.3.A.

Possible Cause:

Excessive heat.

Remedy:

Inspect baffling or cooling air duct. Correct as necessary.

Possible Cause:

Faulty induction system.

Remedy:

Inspect for leaks and faulty valve operation. Consult engine manufacturer’s specifications for proper operation and performance

Possible Cause:

Faulty exhaust system.

Remedy:

Inspect for obstructions in exhaust pipes and mufflers, faulty valve operation. Consult engine manufacturer's specifications for proper operation and performance.

Possible Cause:

Propeller out of track or unbalanced.

Remedy:

Consult propeller manufacturer's manual for specifications. Correct as necessary.

Possible Cause:

Propeller imbalanced or installed incorrectly.

Remedy:

Correct as necessary.

Possible Cause:

Propeller/Engine harmonic resonance.

Remedy:

Consult airframe manufacturer's operations manual. Correct as necessary.

Possible Cause:

Magneto Internal Component Failure:

Remedy:

Consult Champion Aerospace Manual L-1363, Section 3 for specifications and inspections procedures.

Possible Cause:

Points

Remedy:

Inspect for excessive burning, pitting, corrosion, gap setting and general operation. Replace as necessary.

Possible Cause:

Cam

Remedy:

Inspect cam for excessive wear or unevenness that could cause "cam spread". Correct as necessary.

Possible Cause:

Condenser

Remedy:

Inspect for faulty P-lead connection, P-lead stud for over-torqued condition, damaged pigtail connector and damaged grounding. Replace as necessary.

Possible Cause:

Coil

Remedy:

Inspect for cracks, damage to high tension strap or pigtail connector and integrity of windings. Replace as necessary.

Possible Cause:

Distributor Gear

Remedy:

Inspect electrode finger for looseness, gear teeth, shaft. Inspect carbon brush for damage. Replace as necessary.

Possible Cause:

Distributor Block

Remedy:

Inspect distributor towers for evidence of abrasion or excessive burning. Examine rotor gear bushings for wear. Replace as necessary.

Possible Cause:

Rotor shaft at cam slot

Remedy:

Consult Champion Aerospace Manual L-1363, Section 3.3.3.A.

Possible Cause:

Faulty fuel delivery system.

Remedy:

Consult engine manufacturer's manual for specifications and operation. Correct s required.

Possible Cause:

Faulty induction system.

Remedy:

Inspect for leaks and faulty valve operation. Consult engine manufacturer's specifications for proper operation and performance. Correct as required.

Possible Cause:

Faulty exhaust system.

Remedy:

Inspect for obstructions in exhaust pipes and mufflers, faulty valve operation. Consult engine manufacturer's specification for proper operation and performance

Possible Cause:

Incorrect external timing to engine.

Remedy:

Consult engine manufacturer's manual for specifications of ignition timing. Correct as necessary.

Possible Cause:

Incorrect internal timing.

Remedy:

Consult Champion Aerospace Manual L-1363, Section 7.11, for internal timing specifications. Correct as required.

Possible Cause:

Broken rotor shaft at cam slot.

Remedy:

Consult Champion Aerospace Manual L-1363, Section 3.3.3.A.

Possible Cause:

Fouled spark plugs.

Remedy:

Clean spark plugs according to manufacturer's specifications.

Possible Cause:

Incorrect spark plug gap.

Remedy:

Re-gap spark plug to manufacturer's specifications.

Possible Cause:

Faulty spark plug.

Remedy:

Test spark plug according to manufacturer's specifications.

Possible Cause:

Faulty tachometer.

Remedy:

Confirm tachometer accuracy at RPM where magneto drop noted. Correct as necessary.

Possible Cause:

Corrosion on harness lead contacts.

Remedy:

Consult Champion Aerospace Harness Maintenance Manual L-1499 for proper cleaning and inspection procedures. Correct as required.

Possible Cause:

Faulty ignition switch.

Remedy:

Inspect ignition switch for possibility of intermittent grounding and proper operation. Repair or replace as necessary.

Possible Cause:

Faulty condenser.

Remedy:

Consult Champion Aerospace Manual L-1363, Section 3.3.8. Inspect for faulty P-lead connection, broken P lead stud, damaged pigtail connector, and damaged grounding. Replace as necessary.

Possible Cause:

Point gap setting incorrect.

Remedy:

Consult Champion Aerospace Manual L-1363, Section 7.11, for point cap specifications. Correct as required.

Possible Cause:

Retard contact point circuit inoperative.

Remedy:

Inspect and correct as required.

Possible Cause:

Broken rotor shaft at cam slot.

Remedy:

Consult Champion Aerospace Manual L-1363, Section 3.3.3.A.

Possible Cause:

Faulty ignition switch.

Remedy:

Inspect ignition switch for possibility of intermittent grounding and proper operation. Repair or replace as necessary.

Possible Cause:

Broken "P" lead wire.

Remedy:

Repair as necessary.

Possible Cause:

Incorrect external timing to engine.

Remedy:

Consult engine manufacturer's manual for specifications of ignition timing. Correct as required.

Possible Cause:

Faulty Tachometer

Remedy:

Consult engine manufacturer's manual for specifications of ignition timing. Correct as required.

Possible Cause:

Broken rotor shaft at cam slot.

Remedy:

Consult Champion Aerospace Manual L-1363, Section 3.3.3.A.

Possible Cause:

Hold down clamp over torqued.

Remedy:

Torque hold-down clamps to 190-220 in-lbs.

Possible Cause:

Hold down clamps torqued unevenly.

Remedy:

When magneto is reinstalled, be sure clamps are tightened with even pressure.

Possible Cause:

Magneto gasket residue on accessory case mounting pad.

Remedy:

Be sure mounting face is free of gasket residue.

Possible Cause:

Faulty condenser.

Remedy:

Consult Champion Aerospace Manual L-1363, Section 3.3.8, for testing procedure. Replace as necessary.

Possible Cause:

Improper spark plug gap.

Remedy:

Re-gap plugs according to manufacturer's specifications.

Possible Cause:

Fouled spark plug.

Remedy:

Clean spark plug according to manufacturer's specifications.

Possible Cause:

Excessive heat.

Remedy:

Inspect baffling or cooling air duct. Correct as necessary.

Possible Cause:

Improper tension between high tension lead and carbon brush.

Remedy:

Consult Champion Aerospace Manual L-1363, Section 7.8, for high tension lead loading specifications.

Possible Cause:

Faulty coil.

Remedy:

Consult Champion Aerospace Manual L-1363, Section 3.3.6, for specifications and inspection procedures. Replace as necessary.

Possible Cause:

Improper spark plug gap.

Remedy:

Consult Champion Aerospace Manual L-1363 for proper cleaning procedures. Correct as necessary.

Possible Cause:

Faulty spark plug.

Remedy:

Inspect spark plug according to manufacturer's specifications.

Possible Cause:

Fouled spark plug.

Remedy:

Clean spark plug according to manufacturer's specifications.

Possible Cause:

Excessive heat.

Remedy:

Inspect baffling or cooling air duct. Correct as necessary.

Possible Cause:

Timing pin wedged between electrode and distributor block during timing process.

Remedy:

Consult Champion Aerospace Manual L-1363 for proper timing procedures. Replace block and gear assembly.

Possible Cause:

Electrode finger contacting towers.

Remedy:

Inspect and replace as necessary.

Possible Cause:

Improper lubrication of bushing.

Remedy:

Consult Champion Aerospace Manual L-1363, Section 3.3.9, for proper maintenance procedures.

Possible Cause:

Carbon tracking due to excessive carbon brush wear.

Remedy:

Consult Champion Aerospace Manual L-1363, Section 7.8, for high tension lead loading specifications.

Possible Cause:

Bearing not updated to correct configu¬ration.

Remedy:

Consult Champion Aerospace Manual L-1363, Section 3.3.2 and 7.1, for proper maintenance procedure.

Possible Cause:

Improper bearing installation.

Remedy:

Consult Champion Aerospace Manual L-1363, Section 3.3.2 and 7.1, for proper maintenance procedure.

Possible Cause:

Faulty pressurization or filtration system.

Remedy:

Consult engine manufacturer's manual for pressurization system specifications.

Possible Cause:

Excessive or improper solvents or cleaning agents.

Remedy:

Consult Champion Aerospace Manual L-1363 for proper cleaning procedures. Correct as necessary.

Possible Cause:

Worn or fouled spark plugs. Arcing ignition wire.

Test:

Inspect and replace or repair as necessary.

Possible Cause:

Mag Impulse Coupling not operating properly.

Test:

Remove and check for binding, worn or broken impulse coupling parts.

Possible Cause:

Impulse Coupling is magnetized.

Test:

Remove and demagnetize or replace impulse coupling. Inspect engine for magnetized components and demagnetize all such components

Possible Cause:

Low voltage at vibrator input.

Test:

Measure voltage between vibrator terminal marked "in" and the ground terminal while operating starter. Must be at least 8 volts on 12-volt systems, or 13 volts on 24 volt systems.

Possible Cause:

Inoperative or defective vibrator.

Test:

If voltage is adequate, listen for buzzing of vibrator during starting. If no buzzing is heard, either the vibrator is defective or the circuit from the "Output" terminal on the vibrator to the retard (dual contact assembly) magneto is open. Check both "Switch" and "Retard" circuits. Also check for good electrical ground.

Possible Cause:

Retard contact assembly in retard (dual contact) magneto not operating electrically. Engine may kick back during cranking due to advance timing of ignition.

Test:

Retard points may not be closing due to improper adjustment or may not be electrically connected in the circuit due to a poor connection. Inspect retard points to see if they close. Check for proper contact at the "SWITCH" and "RETARD" terminals of retard (dual contact assembly) magneto and at the vibrator. Check wiring.

Possible Cause:

Vibrator-magneto combination not "putting out" electrically.

Test:

Tum engine in proper direction of rotation nation until retard points just open on number one cylinder position. Remove input connection from starter to prevent engine turning, and while holding No. 1 plug lead 3/16 inch from ground, energize vibrator by turning switch to start.
Plug lead should throw a 3/16-inch spark. If spark is weak or missing, try new vibrator. If this does not correct trouble, remove magneto and check for improper internal timing or improperly meshed distributor gears.

Possible Cause:

Magneto improperly timed to engine

Test:

Check magneto-to-engine timing in accordance with Engine Manufacturer's instructions.

Possible Cause:

Advance contact assembly out of adjustment (internal timing off).

Test:

Check magneto timing per paragraph 9.2.10 of ASSEMBLY

Possible Cause:

Retard contacts opening too late.

Test:

Check timing of retard contacts according to paragraph 9.2.10 of ASSEMBLY.

Possible Cause:

Faulty spark plugs.
Faulty ignition leads.

Test:

Try new spark plugs.
Check plug leads for continuity and breakdown.

Possible Cause:

Faulty magneto contact assemblies

Test:

Check magneto contact assemblies for burning out. (Main and Retard.) See PERIODIC MAINTENANCE, paragraph 6.2.1 steps A, B, and C.

Possible Cause:

Carbon-tracked distributor block (21)

Test:

Replace distributor block (21)

Possible Cause:

Magneto out of time

Test:

Check magneto-to-engine timing in accordance with Engine Manufacturer's instructions.

Possible Cause:

Contact assemblies not opening properly.

Test:

Inspect contact assemblies for proper opening. See ASSEMBLY, paragraph 9.2.10.

Possible Cause:

Faulty plugs or leads
No drop-off noted – open capacitor

Test:

Check plugs and leads.
Check capacitor as specified in GENERAL OVERHAUL, paragraph7.2.5.

Possible Cause:

Carbon-tracked distributor block (21)

Test:

Replace distributor block (21)

Possible Cause:

Worn or fouled spark plugs. Arcing ignition wire.

Test:

Inspect and replace or repair as necessary.

Possible Cause:

Mag Impulse Coupling not operating properly.

Test:

Remove and check for binding, worn or broken impulse coupling parts.

Possible Cause:

Impulse Coupling is magnetized.

Test:

Remove and demagnetize or replace impulse coupling. Inspect engine for magnetized components and demagnetize all such components

Possible Cause:

Low voltage at vibrator input.

Test:

Measure voltage between vibrator terminal marked "in" and the ground terminal while operating starter. Must be at least 8 volts on 12-volt systems, or 13 volts on 24 volt systems.

Possible Cause:

Inoperative or defective vibrator.

Test:

If voltage is adequate, listen for buzzing of vibrator during starting. If no buzzing is heard, either the vibrator is defective or the circuit from the "Output" terminal on the vibrator to the retard (dual contact assembly) magneto is open. Check both "Switch" and "Retard" circuits. Also check for good electrical ground.

Possible Cause:

Retard contact assembly in retard (dual contact) magneto not operating electrically. Engine may kick back during cranking due to advance timing of ignition.

Test:

Retard points may not be closing due to improper adjustment or may not be electrically connected in the circuit due to a poor connection. Inspect retard points to see if they close. Check for proper contact at the "SWITCH" and "RETARD" terminals of retard (dual contact assembly) magneto and at the vibrator. Check wiring.

Possible Cause:

Vibrator-magneto combination not "putting out" electrically.

Test:

Tum engine in proper direction of rotation nation until retard points just open on number one cylinder position. Remove input connection from starter to prevent engine turning, and while holding No. 1 plug lead 3/16 inch from ground, energize vibrator by turning switch to start.
Plug lead should throw a 3/16-inch spark. If spark is weak or missing, try new vibrator. If this does not correct trouble, remove magneto and check for improper internal timing or improperly meshed distributor gears.

Possible Cause:

Magneto improperly timed to engine

Test:

Check magneto-to-engine timing in accordance with Engine Manufacturer's instructions.

Possible Cause:

Advance contact assembly out of adjustment (internal timing off).

Test:

Check magneto timing per paragraph 9.2.10 of ASSEMBLY

Possible Cause:

Retard contacts opening too late.

Test:

Check timing of retard contacts according to paragraph 9.2.10 of ASSEMBLY.

Possible Cause:

Faulty spark plugs.
Faulty ignition leads.

Test:

Try new spark plugs.
Check plug leads for continuity and breakdown.

Possible Cause:

Faulty magneto contact assemblies

Test:

Check magneto contact assemblies for burning out. (Main and Retard.) See PERIODIC MAINTENANCE, paragraph 6.2.1 steps A, B, and C.

Possible Cause:

Carbon-tracked distributor block (21)

Test:

Replace distributor block (21)

Possible Cause:

Magneto out of time

Test:

Check magneto-to-engine timing in accordance with Engine Manufacturer's instructions.

Possible Cause:

Contact assemblies not opening properly.

Test:

Inspect contact assemblies for proper opening. See ASSEMBLY, paragraph 9.2.10.

Possible Cause:

Faulty plugs or leads
No drop-off noted – open capacitor

Test:

Check plugs and leads.
Check capacitor as specified in GENERAL OVERHAUL, paragraph7.2.5.

Possible Cause:

Carbon-tracked distributor block (21)

Test:

Replace distributor block (21)

Possible Cause:

Worn or fouled spark plugs; arcing ignition lead

Test:

Inspect and replace or repair as necessary

Possible Cause:

Impulse Coupling not operating properly

Test:

Remove and check for binding, worn or broken impulse coupling parts. Ensure D6LN-2031 model magnetos incorporate latest "Heavy Spring" Impulse Coupling Assembly.

Possible Cause:

Impulse Coupling is magnetized

Test:

Remove and demagnetize or replace impulse coupling. Inspect engine for magnetized components and demagnetize all such components

Possible Cause:

Low voltage at vibrator input

Test:

Measure voltage between vibrator terminal marked "in" and the ground terminal while operating starter. Must be at least 8 volts on 12 volt systems, or 13 volts on 24 volt systems.

Possible Cause:

Inoperative vibrator

Test:

If voltage is within specification, listen for buzzing of vibrator during starting. If no buzzing is heard, either the vibrator is inoperative or the circuit from the "Output" terminal on the vibrator to the switch and magneto points is open. Check both "Switch" and "Retard" circuits. Check for continuity from the BO terminal, through the switch and through both the main and retard magneto points.

Possible Cause:

Retard contact assembly in retard (dual contact) magneto not operating electrically. Engine may kick back during cranking due to advance timing of ignition

Test:

Retard points may not be closing due to improper adjustment or may not be electrically connected in the circuit due to a poor connection. Inspect retard points to see if they close. Check for proper contact at the “SWITCH” and “RETARD” terminals of retard (dual contact assembly) magneto and at the vibrator. Check wiring.

Possible Cause:

Vibrator-magneto combination not "putting out" electrically

Test:

Turn engine in the normal direction of rotation until retard points just open on No. 1 cylinder position. Remove input connection from starter to prevent engine turning, and while holding No. 1 plug lead 3 / 16 inch from ground, energize vibrator by turning switch to START. Plug lead should throw a 3/16-inch spark. If spark is weak or missing, install new vibrator. If this does not correct trouble, remove magneto and check for improper internal timing or improperly timed distributor gears.

Possible Cause:

Magneto improperly timed to engine

Test:

Check magneto-to-engine timing according to the Engine Manufacturer's instructions. Inspect contact assemblies according to instructions in Section 6- 2.1 and adjust and replace parts as necessary.

Possible Cause:

Main contact assembly out of adjustment (internal timing off).

Test:

Check magneto internal timing according to instructions in Section 9-2.8.

Possible Cause:

Retard points opening too late.

Test:

Check timing of retard points according to instructions in Section 9-2.8.

Possible Cause:

Worn or fouled spark plugs

Test:

Install new spark plugs.

Possible Cause:

Worn ignition leads.

Test:

Check plug leads for continuity and breakdown.

Possible Cause:

Carbon tracked distributor block.

Test:

Replace distributor block

Possible Cause:

Worn or fouled magneto contact assemblies.

Test:

Check magneto contact assemblies for burning, melting or contamination according to instructions in Section 6-2.1.

Possible Cause:

Magneto to engine timing incorrect.

Test:

Check magneto-to-engine timing according to the Engine Manufacturer's instructions. Inspect contact assemblies according to instructions in Section 6- 2.1 and adjust and replace parts as necessary.

Possible Cause:

Magneto to engine timing incorrect.

Test:

Check magneto-to-engine timing according to the Engine Manufacturer's instructions. Inspect contact assemblies according to instructions in Section 6- 2.1 and adjust and replace parts as necessary.

Possible Cause:

Contact assemblies not opening properly.

Test:

Inspect contact assemblies for proper opening according to instructions in Section 9-2.8.

Possible Cause:

Main contact assembly out of adjustment (internal timing off).

Test:

Check magneto internal timing according to instructions in according to instructions in Section 9-2.8.

Possible Cause:

Faulty plugs or leads.

Test:

Check plugs and leads.

Possible Cause:

No drop-off noted -- open switch connection.

Test:

Check capacitor according to instructions in Section 7-2.5.

Possible Cause:

Carbon tracked distributor block.

Test:

Replace distributor block

Possible Cause:

Faulty spark plugs.

Test:

Replace spark plugs

Possible Cause:

Frayed shielding at spark plug terminal, magneto cover, or intermediate point on harness lead.

Test:

Replace ignition lead

Possible Cause:

Inadequate shielding ground at spark plug terminal or magneto cover.

Test:

Remove and replace inner ferrule according to instructions in Section 9-3.