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Yamaha 2.5hp 4 stroke Plugs fouling


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Howdy all! 

 

You may or may not remember me asking for advice about buying a boat and living on it last year- well I've just finished sailing around Northland and Great Barrier and Im now living aboard in Auckland. Life is much better when your outboard isn't almost dying every time you try to get home. The outboard ran great for the last 3 weeks but has now developed oil fouling on the spark plugs. I've changed them twice in 10 days already, I was hoping it was just an issue from maybe leaving it on its side but I would have thought the oil would have burned off by now. I only use it for about 3 minutes at a time going to and from my boat. its a '08 Yamaha F2.5 4 Stroke. Any advice on what to try next would be really appreciated. 

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possibly the run time is too short for the engine to get warm enough? perhaps the plug you are using is in the wrong heat range? Faulty plugs? Sump over full? broken / damaged oil ring? Take it for a longer run and see if the problem still persists. From what you have written, it only started since you have been doing short runs.

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While we're here, I live aboard and the putt put is in constant use. 4 stroke 4 horse. Every few months it dies and I can get it going by draining some fuel from under carb. I hoped with time it would sort itself out, but that hasn't happened.  Ideas?

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water in the  bowl from either condensation, rain entering somehow or a contaminated fuel supply- or a bit of grunge that gets sucked into the jets but since you empty the bowl that should clear it.

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2 hours ago, Black Panther said:

While we're here, I live aboard and the putt put is in constant use. 4 stroke 4 horse. Every few months it dies and I can get it going by draining some fuel from under carb. I hoped with time it would sort itself out, but that hasn't happened.  Ideas?

Drain the tank, check for water?

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3 hours ago, NoMaker said:

Howdy all! 

 

You may or may not remember me asking for advice about buying a boat and living on it last year- well I've just finished sailing around Northland and Great Barrier and Im now living aboard in Auckland. Life is much better when your outboard isn't almost dying every time you try to get home. The outboard ran great for the last 3 weeks but has now developed oil fouling on the spark plugs. I've changed them twice in 10 days already, I was hoping it was just an issue from maybe leaving it on its side but I would have thought the oil would have burned off by now. I only use it for about 3 minutes at a time going to and from my boat. its a '08 Yamaha F2.5 4 Stroke. Any advice on what to try next would be really appreciated. 

Is it definitely oil fouling and not fuel?

What's the oil level like? Could the piston rings be buggered?

If fuel: Choke on for too long? Starting on open throttle?

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If its only running for 3 minutes at a time, irregularly, the fouling is more likely from a very rich fuel mixture.

The simplest fix is to take it for a good ten-minute thrashing every week or so.  This will will burn off any fouling on the plugs and help the longevity of the engine as well - running rich means the cylinder bore is always wet with fuel that dilutes any oil and ends up accelerating bore and piston ring wear.  Ironically, this leads to oil fouling...

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5 hours ago, Bad Kitty said:

Drain the tank, check for water?

That's the obvious one, but I run it dry at least once a week. I've cleaned everything I can think of, is condensation a possibility? 

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In  both cases I'd be dropping the fuel bowl and looking for a glob of something as said above ,  check float level and float valve. Blow out the fuel line ,inspect the tank.

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Some good answers already. I can only add a little extra to a few of them.
Ensure spark gap is correct. 0.4 to 0.6mm. The plug should be a BR6HS
When you lay the engine down, you always ensure the cylinder is pointing up. In other words, the spark plug is at the top.
Make sure you are using the correct oil the manufacturer says to use and ensure the system is not over fill. There is  little "window" on the side to ensure correct level. 10W-30 or 10W-40 is the norm.
There is an Oil blowby scavenging system that uses a part of the head to remove the oil droplets from the fumes and only allow the fumes back to the Carb. That could be worth a check that it is not clogged in the hose. Unlikely, but....
Make sure you are using the correct fuel Octane rating, which is 91 for these.
Does the engine Idle nicely and does it run at full Throttle OK? Idle is quite fast for these. Normally 1800 to 2000RPM
Idle mixture screw is set by screwing in till it stops, then backing off 2.5turns should have you close to spot on. If the motor will not idle sweetly, that is usually a sign the float in the fuel bowl needs to be adjusted.


 

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Yamaha F2.5 4 Stroke.. These engines are very sensitive to dirty fuel. The idle jets are tiny.  Last Christmas I drained the tank,  cleaned the mesh filter and blew out the jets four times before it would run reliably.

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