1972 100 hp johnson no spark

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Where do I start have no spark on all four cylinders

 

[faztbullet]

1) Make sure you have good battery and fully charged
2) Remove coil wire from distributer cap and install spark gap tester
3) Set tester at 1/2 gap and crank engine, if you have spark problem is in cap/rotor
4) Check voltage at purple wire as it cannot fall below 9-1/2 volts when cranking, if not service starter/battery cables or test battery amp output
5) Using a DVA adapter test the output on blue wire to coil as it should be 200V or higher when cranking
6) If still no fire, remove the blk & wht wires at bullet connectors. Turn key on and strike these wires together and pack should spark. If it fire the problem is in sensor or sensor wiring. If no spark the pack is bad.