1991 Yamaha Outboard Factory Service Manual 9.9 and 15 HP, Page 108Get this manual
12345 Remove the fuse holder and fuse from the testerTake out the voltage selectorSet the notch to the voltage indicated on the peripheryRemount the fuse and fuse holderHook up the coil tester to the ignition coil as shown
Minimum spark gap: mm (0.31 in) NOTE: _ The performance of the ignition coil will be affected by heatThe spark test should therefore be performed at intervals of to 10 minutes for correct test results