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what would cause a wet plug? trigger / switchbox / coil - what r the symptoms?

FstaRockr Burns

Regular Contributor
My lower plug on my 3 cyl 60 mariner is always wet, the middle one so so - top one burns perfectly.. like it gets progressively worse -

Ive always had spark on all three - checked that many time over with timing light..

would a bad trigger fire one or 2 cylinders at the wrong time causing incomplete burning?

and what would a faulty switch box do - not fire at all?


I tested the pri and sec side of all 3 coils - they were exactly the same readings -

or could a stator thats not outputting enough volts cause weak spark?

bit rainy here and motor in pieces, but trying to put her back together this weekend then ill do some ignition troubleshooting -

fyi - motor wd always start no problem, but has a high speed miss and lacks about half the power - and takes time to reach speed..

alot of soot on drive shaft - so some fuel aint getting burnt. new plugs all round and all connections incl ground checked - carbs cleaned 6 times now - replaced all filters and hoses.. pump seems to send thru more than enough fuel.. diaphragm is not torn - still in good shape - battery charged (not agm type) - regular lead acid.. 8 months old..
 
A wet plug could be no spark or weak spark or could even be caused by a carb flooding.

So if you are "getting spark" then try adjusting the carb(s) that feed the lower two cylinders - they may be running very rich (could possibly need a rebuild if you have float/flooding issues). The carb adjustment is an "easy do it yourself without much troubleshooting solution".

Now, despite having spark you may have a "weak spark" - often numbers like "jumping a 7/16" gap" etc get tossed around. Many discount auto places have the spark testers that look like a sparkplug where you screw out the contact to whatever gap and then see if "she jumps".

A weak spark could be caused by a cracked sparkplug coil (which could also result in intermittent "no spark" sometimes while "great spark" at others).

Weak spark could also be the fault of the switchbox not sending enough power to the spark plug coils (due to defect of some sort). Likewise a weak stator may not be producing enough power to adequately fire the plugs downstream.

The trigger is an "unlikely candidate" - it either works or doesn't - so you will get spark or no spark - it doesn't effect spark intensity, and because of it's design it can't/won't time one or two cylinders correctly but not the third etc.

The time to reach speed and intermittent miss at high speed would first cause me to investigate the spark plug coils. I would remove them, really clean them up well and look for cracks - bad coils could cause both of those issues.

Having said that, a fuel issue - either partly clogged carb(s) or a bad gasket/seal allowing fuel to escape could also be to blame.

So start with the "easiest" things to correct (that don't immediately cost money - adjust the carb(s), inspect the coils, look for an oily goop around any gaskets or seals on the crankcase or intake) and move on from there once you have eliminated the easy stuff as the possible cause.
 
thanks galamb! very interesting info - will try get motor back together again this weekend (if the weather and gf allows! - the two kinda go together lol).. luckily i have a bunch of spares so can do some tests..

my carbs seems fine cos when i apply pressure none leaked - when they leak its very visible as the fuel pours out the mouth (when slightly tilted).. so i think i can rule out over fueling.. but since it affects the bottom and middle carb that DOES point to a carb issue - fyi i did see a guy test a 4 cyl trigger on youtube, where 3 of the 4 plug wires were firing on multiple cylinders and one seemed fine..

anyway - ill do some dva tests and checks once shes back up and running..

thanks again!
 
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