Yamaha F100B F100C Outboards Factory Service Manual, Page 324Get this manual
TRBL SHTG
Troubleshooting
Symptom: Engine cranks, but will not start Check the ignition system Check the fuel system Check the compression pressure of the power unitCheck that the spark plugs produce sparks
WARNING
Do not touch any of the connections of the spark gap tester leads Do not let sparks leak out of the removed spark plug caps Keep flammable gas or liquids away, since this test can produce sparksCheck the ignition spark using the spark gap tester