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Ted G.
Ted G., Rigger, Diagnostician
Category: Boat
Satisfied Customers: 6159
Experience:  40 years boating, Safe boating instruct., Offshore Race promoter, Failure Analysis, Expert Witness
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I have about a 1980 jonson 15hp that only fires one coil,

Customer Question

i have about a 1980 jonson 15hp that only fires one coil, the bottom coil tries to fire but at isle only and intermittent, does thios still have points?
JA: Sometimes things that you think will be really complicated end up being easy to fix. The Marine Mechanic I'm going to connect you with knows all the tricks and shortcuts. Tell me a bit more about what's going on so the Marine Mechanic can help you best.
Customer: only runs on one cylinder, and is a twin. no spark at one cylinder and its not a coil
JA: Is there anything else the Marine Mechanic should be aware of?
Customer: no
Submitted: 3 months ago.
Category: Boat
Expert:  Ted G. replied 3 months ago.

It is likely that the magnets under the flywheel have come loose and are either broken or stuck together. Basically the coil is supposed to fire when there is a gap between the magnets, on yours there are two so you get two fires per revolution. But when the magnets break or slip around and touch, there is only one gap, so only one fires. You need to pull the flywheel to check.