1990 Mariner 75hp 3 cylinder missing

[billnorfolk]

Hi i have a 75hp Mariner ,3 cylinder clam shell hood ser number 9483083 Belgium.We have done extensive work on the fuel system and engine was running good ,a couple of weeks ago suddenly started missing on top cylinder ,its got new plugs and leads so thought it must be one of the three coils ,this morning have changed coil but made no difference still no firing on top cylinder swaped leads about but still no spark from lead on top cylinder ,any ideas where we go next not had a full days running since we bought it .

[billnorfolk]

Would the problem point to the CDI box would you think .

[SilverFox579]

Holiday weekend here Bill, replies may be a bit slower than usual.

[billnorfolk]

Same hear in UK ,people flying off everywhere . Looks to be wet and cool hear ,bet California would like some of our rain.

[EuropeanAM]

Stator, trigger, or switchbox are all possibilities.

Testing (as per the Mercury Service Manual) is required to determine the failure.

[billnorfolk]

Stator, trigger, or switchbox are all possibilities.

Testing (as per the Mercury Service Manual) is required to determine the failure.

Thanks Don will run some tests see what comes up .

[billnorfolk]

One thing that is throwing me ,all the wiring diagrams show 4 terminals used on switch box ,hear is a picture of mine showing only 3 used . End terminal showing a red wire to stator in wiring diagram is empty with a cap on as if never been used .No loose wires anywhere ,engine has run on all three cylinders in the past ,but why show 4 terminals in use on wiring diagram

[billnorfolk]

Seems its had a new stator at some time ,a red one with an adapter that only uses 1 wire to switch box ,blue so that mystery solved. Ran some tests yesterday and determined that feed to top coil is non to intermittent so have ordered new switch box see if we have success with that ,fingers crossed.

[EuropeanAM]

You're on the right track. Based on what information you've provided, it's likely EITHER the switchbox, OR the trigger.