Reply To: 6 hp Johnson no fire

[Don]

You can try putting one of those inexpensive “inline neon spark testers” in between the spark plug and ignition wire while the engine is running. You can get these at many auto parts stores inexpensively. Not a fool proof test, but can be helpful… Try it on the top cylinder first so you will know how intense/frequent the neon light should be…It is best to do this test when the sun is going down. Be sure the connections don’t accidentally get grounded to the block. Just because the plugs are new, doesn’t mean they are any good…Try swapping the plugs to see if the upper cylinder stops firing with the lower cylinder’s plug installed.
To answer your question, the ignition system may have enough power to fire a plug when grounded to the block, but it takes considerably more energy/voltage to fire it in the combustion chamber under compression….