hotrod180
FRIEND
Port Townsend, WA
From AMS's troubleshooting page, which I linked earlier:
"Most “bad mag checks” are spark plug related. The spark plug is fouled and shorted to ground or is open and the magneto, which is functioning normally, is unable to fire it. A typical bad plug will cause an immediate drop of 250 or more RPM, at the mag check. The key indicator is the suddenness of the drop."
and re checking individual plugs:
"Pick out lead deposit clinkers, inspect the barrel for cracked insulator, inspect the nose core for cracks.Clean and inspect the plug (correct gap for most plugs is .015” to .019” consult your plug specifications).
Take an OHM Meter and measure the resistance value from the connection in the bottom of the barrel to the clean center electrode at the firing end, electrode must be bare metal.
A new Champion plug will have a value of 800 to 1200 OHMS. New Tempest (formerly Unison-Autolite) will measure 1000 OHMS. Replace any plug above 5000 OHMS.
A spark plug bomb tester can test a bad plug and lead you to conclude it is serviceable. The OHM Meter check is simple, readily available, and amazingly accurate in finding misfiring plugs."
"Most “bad mag checks” are spark plug related. The spark plug is fouled and shorted to ground or is open and the magneto, which is functioning normally, is unable to fire it. A typical bad plug will cause an immediate drop of 250 or more RPM, at the mag check. The key indicator is the suddenness of the drop."
and re checking individual plugs:
"Pick out lead deposit clinkers, inspect the barrel for cracked insulator, inspect the nose core for cracks.Clean and inspect the plug (correct gap for most plugs is .015” to .019” consult your plug specifications).
Take an OHM Meter and measure the resistance value from the connection in the bottom of the barrel to the clean center electrode at the firing end, electrode must be bare metal.
A new Champion plug will have a value of 800 to 1200 OHMS. New Tempest (formerly Unison-Autolite) will measure 1000 OHMS. Replace any plug above 5000 OHMS.
A spark plug bomb tester can test a bad plug and lead you to conclude it is serviceable. The OHM Meter check is simple, readily available, and amazingly accurate in finding misfiring plugs."