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

[Anonymous]

A good place to start is the spark plugs. Replace them or swap them
hole for hole and see if the problem follows the suspect plug.
Next is a compression check. If you don’t have a compression gauge, you can barrow
one from a auto parts store.
Don’t worry about how high the reading is, but how close the cylinders are to each other.
Next check the ignition. Someone else will have to help with this as I’ve never worked
on a motor this new. I’m not sure if it has points or solid state ignition.
Good luck with it.

Steve A W