90 hp Mercury misses on & off upon acceleration

pecheux

pecheux

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This is on behalf of a friend: He has a 2 years old 90 HP 4 cycle Mercury outboard on a 16 footer which he uses hardly 10 hours per summer season, the rest of the time the boat sits in his backyard with built in gas tank at 1/4 filled so I do presume is gas gets staled. I told him this is a no no and he wont do it again lol. He filled it and took it out last week and tells me there is still the occasional misfiring of the motor upon acceleration. It occures unexpectedly and on & off. He had it tuned by Merc dealer last year so very few hours have been added on since. Can this sputtering be due to stale petrol or condensation water in the built in gas tank ? Tx
 
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baylinerbuff

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Re: 90 hp Mercury misses on & off upon acceleration

Low fuel levels, hence condensation in the tank and stale gas stored for a long period of time is a bad combination which is probably the cause of the occasional misfiring.
 
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thefairlaneman

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Re: 90 hp Mercury misses on & off upon acceleration

Please tell me he didnt just put several gallons of fresh gas into a tank that most was likely contaminated and old? YOu have to dump the couple of gallons that have water or other contaminates in it OUT FIRST then put in some fresh gas....which was it?.
 
pecheux

pecheux

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Re: 90 hp Mercury misses on & off upon acceleration

thefairlaneman said:
Please tell me he didnt just put several gallons of fresh gas into a tank that most was likely contaminated and old? YOu have to dump the couple of gallons that have water or other contaminates in it OUT FIRST then put in some fresh gas....which was it?.
Click to expand...

Since water stays at the bottom, and there seems to be no dain plug on the buit in gas tank. How can the stale gas be pumped out "to the last drop" ??
Tx
 
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Laddies

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Re: 90 hp Mercury misses on & off upon acceleration

Remove the fuel sender and pump out the hole, use a new gasket opon replacing.
 
pecheux

pecheux

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Re: 90 hp Mercury misses on & off upon acceleration

Laddies said:
Remove the fuel sender and pump out the hole, use a new gasket opon replacing.
Click to expand...

Does the fuel sender reach the bottom of the tank ? Or what about using a hand held syphon pump making sure the tip is a the bottom of the tank ?
 
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Laddies

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Re: 90 hp Mercury misses on & off upon acceleration

That will work, it helps to have a piece of copper tube on the end and a good flashlight to see.
 
pecheux

pecheux

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Re: 90 hp Mercury misses on & off upon acceleration

Laddies said:
That will work, it helps to have a piece of copper tube on the end and a good flashlight to see.
Click to expand...

On behalf of my friend ... thank you ... much appreciated.
 
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