Mercury 25hp 2 Stroke one spark only

[rib-x450]

Does any one know:

I have a 25hp 1988 2 stroke, the engine only sparks on one cylinder?

I have changed the plug and coil , one has a good fat spark one has nothing?

Is the switvh box a possible fault, or would both not plugs not spark.

Has anyone got a switch box for this engine, I can buy or borrow to try it?

Any help greatly appreciated.

[Locozodiac]

Could you post pics of both engine sides to see CD unit and plug coils and to look for a compatible engine type ?

[Downhilldai]

Is the HT lead ok?

[rib-x450]

I have checked the earth of both coils, is there on sensor per coil or two from the flywheel?

I would have thought CDI would work or not ........... can believ one side is ok one isnt?

Any more thoughts?

[ian parkes]

Take the coil lead and plug from the side that is working OK and fit it the other side , that will at least rule out the chance of a second faulty coil lead or plug.