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Old 18 April 2016, 08:23   #11
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try new spark plugs, and examine health of ignition leads - disconnect from coil packs and clean connectors on both ends.

Run engine until it bogs, then kill engine and pull the plugs - tell us the colour of each of the spark plug tips on each cylinder and smell for / look for wet unburnt fuel.

If one cylinder shows inconsistent burn, swap plugs and spark leads over with another and repeat:
If different plug now fouls you have problem with that lead or plug.
If same plug still fouls you have a problem with the ignition circuit (coil pack, trigger from CDI) or carb/fuel line on that one cylinder.


Had a 55 mariner with same symptoms - started fine and spark visible when test cranking on shore. Turned out to be a hairline crack in the spark plug insulator neck.
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Old 18 April 2016, 08:25   #12
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Can you have an assistant pump the fuel bulb when it starts to bog? This would rule out issues with fuel pump diaphragms
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Old 18 April 2016, 10:32   #13
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Plugs are brand new.. Tried old plug in cyl 3..no difference.. Yes friend pumped bulb during bogging.. No change.

Did wot run, top two were nice tan, bottom wet fuel, like it wasn't firing at high rpms.. Thing is jumping all over the place..

All fire perfectly at idle.. Think timing is wrong somehow..

Tx for the suggestions so far.. Think I've covered fuel supply and some base settings..

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Old 18 April 2016, 10:53   #14
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is the poor running only higher up the rev range. how does it idle. is it repeatable or reproduceable? Is the bottom plug consistently wet and the others a nice tan. Sounds very electical?? Nik
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Old 18 April 2016, 10:54   #15
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Plugs are brand new.. Tried old plug in cyl 3..no difference.. Yes friend pumped bulb during bogging.. No change.

Did wot run, top two were nice tan, bottom wet fuel, like it wasn't firing at high rpms.. Thing is jumping all over the place..

All fire perfectly at idle.. Think timing is wrong somehow..

Tx for the suggestions so far.. Think I've covered fuel supply and some base settings..

Sent from my SM-G900M using Tapatalk
Check the resistances and examine for cracking in the coils if you haven't already.

I have seen cases where modules work fine when cold, then when warm, they expand a little bit and the spark randomly grounds out.

Maybe run the engine in the dark and look for any arc'ing?
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Old 18 April 2016, 10:55   #16
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Bottom plug been wet .. Haven't swapped coils yet.. Only back at boat in a week about.. Really scratching head..

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Old 18 April 2016, 10:57   #17
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I did crank it at night, saw some arcing near coil ground wires and another near plugs.. Rubber looks good tho.. Looked for cracks everywhere.. Stumped. Ran so good just the other day..

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Old 18 April 2016, 10:59   #18
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Maybe sync link is way out? On front cover it says to set Max cranking degrees and then carb cam pickup just before the big slope to open carbs, but it doesn't specify whether to do that with Max stop touching or what...



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Old 18 April 2016, 11:11   #19
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I did crank it at night, saw some arcing near coil ground wires and another near plugs.. Rubber looks good tho.. Looked for cracks everywhere.. Stumped. Ran so good just the other day..

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I have seen that before with automotive plug wires. The insulation has degraded with age and petroleum exposure. You will need to replace the defective spark plug wires. You may have to crimp your own. Keep in mind, most marine spark wires are simply copper cored...NOT automotive-style carbon core.

You may want to redo the grounding. Sand the surface of the attachment and check for high resistance.
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Old 18 April 2016, 11:13   #20
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Reground and cleaned all connections.. Sprayed down with switch cleaned and sanded surfaces

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