1997 Johnson/Evinrude EU 25, 35 HP 3-Cylinder outboards Service Manual, Page 111Get this manual
Output Tests All cranking output tests must be performed with spark plugs installed and torqued in the cylinder headIf necessary to remove the spark plugs, be sure to keep the spark tester away from open spark plug holes&
STEPTOTAL OUTPUT TEST
& To avoid electrical shock, do not handle ignition coil or spark
tester during cranking tests
1Twist and remove all spark plug leads
2Adjust the gap on the spark tester to 3a in(9 mm)Connect tester leads to the spark plug leadsSecure tester clip to clean engine ground(51 mm) from any metal surface