Yamaha 25BMH 30HMH Factory Service Manual, Page 396Get this manual
IGNITION SYSTEM
E (4) Crank the engine and observe the spark through the discharge window of the ignition testerNOTE: If there is no spark or the spark is weak, check spark plug cap, ignition coil, pulser coil, charge coil and CDI unit If good spark is obtained, the problem is not with the ignition system, but possibly with the spark plug(s) or another component
CHECKING THE SPARK PLUG CAPS