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Old 14 April 2011, 14:49   #1
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Country: UK - England
Town: Rustington
Boat name: hirofumi
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Length: 5m +
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60 HP Mariner Bigfoot sparkplug problems

A while ago I was motoring back to the marina when the engine suddenly slowed - sounding as if it was only firing on 2 of the 3 cylinders and this meant that I could only make 6 knots. Changed the plugs and problem solved. However, with only about 15 hours running on the new plugs the problem recurred. This time I changed the plugs whilst at sea and again problem solved. I showed the used plugs to a mechanic (not a marine mechanic) friend of mine and he said that they were excessively oily, to clean and re-use them OR to try some hotter burning plugs. What do you guys think? I'm currently using the recommended NGK BP8H-N-10 plugs. If I need hotter ones can anyone tell me what to get? Thanks in anticipation of your words of wisdom.
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Old 14 April 2011, 14:59   #2
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It could be the plugs but its more likely your air mixture is wrong, or the air intake is blocked. Does it idle well or sluggishly?

Ideally your plugs should be a light brown
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Old 15 April 2011, 06:53   #3
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Many thanks Neil, It has always been a bit lumpy on tickover - sometimes cutting out at extremely low revs when in or out of gear. I'll check the air intake as you suggest. Hopefully that will sort the problem. Thanks again.
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Old 15 April 2011, 09:57   #4
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you have the correct factory recommended s/plugs fitted,what colour spark plug electrodes? is the timming correct ? (checked with a strobe light?) are the carbs syncronised?does it run ok if you keep preasure on the primer bulb?
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