Spark plug fouled in 2015 ProXS Optimax 250

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olefisherman456

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not on a boat motor but it happened with a 350 chevy with a really good motor. very frustrating. on a 40 hp merc that i owned i replaced the plugs and one was bad. new plug had to take to a shop after scoping it out for about 40 min said do you have the old plugs? took out the one from the missing cyl . hwo far can you throw a new sparkplug?
 

jerry shack

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I have seen this before, is it the number 6 cylinder ? However do not run that motor any more until you do a compression test or take it to a dealer.
 

Ronc4773

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Be sure and trim up with prop high, still getting water exiting. Not all plugs are firing at idle. Oil collects on log idles
 

poss0289

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I have seen this before, is it the number 6 cylinder ? However do not run that motor any more until you do a compression test or take it to a dealer.
It was the #3 cylinder, I plan on taking it in this weekend. They were not gapped correctly when I pulled them all, they were at .032 and should have been between .042 - .044
 

OldDude

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Ronc4773... X2.

The exhaust bypass on the engine needs to be out of the water at idle so it can breathe or any Optimax will foul plugs all day long. Trim it up sitting moving at idle until the bypass is out of the water... then trim down to take off...

I think it's called the exhaust bypass...😔
 

poss0289

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Ronc4773... X2.

The exhaust bypass on the engine needs to be out of the water at idle so it can breathe or any Optimax will foul plugs all day long. Trim it up sitting moving at idle until the bypass is out of the water... then trim down to take off...

I think it's called the exhaust bypass...😔
I did not know that, I will definately have to keep that in mind
 

poss0289

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I have seen this before, is it the number 6 cylinder ? However do not run that motor any more until you do a compression test or take it to a dealer.
Actually I was wrong, I thought it was cylinder # 3 but it was # 6 with no compression. Luckily Mercury is going to cover the cost to fix it. Still not sure what caused it.
 

jerry shack

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Actually I was wrong, I thought it was cylinder # 3 but it was # 6 with no compression. Luckily Mercury is going to cover the cost to fix it. Still not sure what caused it.
It's called cold scuffing, when the motor is not warmed up enough and it gets put under a load and there is a thermostat that gets stuck open the cold water does not let the piston swell and aluminum from the piston gets on the injector and you have a melt down, at least that's what I was told by Mercury.
 

Andrebass

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Is this only on 2 strokes or is 4 stroke able to have this problem? I had one time when I got the boat, I left the motor all the way down and started it and some smoke came out of exhaust and sounded different. that was the only time I seen smoke like that.
 

jerry shack

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Is this only on 2 strokes or is 4 stroke able to have this problem? I had one time when I got the boat, I left the motor all the way down and started it and some smoke came out of exhaust and sounded different. that was the only time I seen smoke like that.
It's only on the Opti Max Pro SX 250's 2 cycle motors. If you had your motor tilted all the way up till it stopped and was there for awhile sometimes the oil left in the valve cover seeps down on a open valve and into the cylinder it would smoke just at start up for a second or two.
 
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