Re: 1974 Johnson 15 hp runs on 1 cyl at low speed

[Don]

Have you done a cranking spark check on the engine? It should be able to jump a 1/4" gap on each cylinder while cranking. Don’t worry too much about the cracked external coil, this is not uncommon and does not necessarily mean the coil is bad. Garry makes a good point about the primary leads coming from under the flywheel, these can get frayed, split, shorted to the mag plate easily. You may see/hear an arcing coil more easily by running in the dark, but shorted primary leads probably won’t be visible.
For now, let’s start at the beginning, spark and compression test.