Oil in air intake of outboard.

[pandos]

I have a mariner 2.5hp. on many occasions oil got into the cylinder and pours out of the air intake.

I managed to get it to be useful by carrying upright, but now I have a different car so that's no longer possible.

I carefully carried it home from the boat laying on its side (with the correct side upwards) and yet oil is now pouring from the intake.

Is this just a feature of these engines of is there something that can be fixed...it's a real pain...

 

[Ian_Edwards]

Assuming that the outboard runs well, the only way oil can get into the carburetor is most likely through the crankshaft breather hose.
From there it can get into the cylinder, if the inlet port is open.
There's a remote possibility that it could get into via a valve stem, but if that was the case you'd have other problems and would probably see blue smoke from the exhaust.
The only way I can see that happen is if the outboard is stored or transported the wrong way up.
The tiller arm must always be on top if stored or transported.
I know you say that you say that it's transported the right way up ..... but I don't see any way the oil can get in any other way, Unless you are driving like mad Max in an F1 car and the the G forces are forcing the oil up the crank case breather tube .

Could you please check that you are transporting the outboard with the tiller arm up, I've always found that counter intuitive, because the outboard is more stable tiller arm down.

The Service manual can be found here:
Google Search

I have electronic copies of both the users manual and the Service/Workshop manuals as .pdf's, but they are bit files 19 MB +.
PM me with your email address if you have problems down load them and I' try and forward them to you, but the link should work.

 

[pandos]

Assuming that the outboard runs well, the only way oil can get into the carburetor is most likely through the crankshaft breather hose.
From there it can get into the cylinder, if the inlet port is open.
There's a remote possibility that it could get into via a valve stem, but if that was the case you'd have other problems and would probably see blue smoke from the exhaust.
The only way I can see that happen is if the outboard is stored or transported the wrong way up.
The tiller arm must always be on top if stored or transported.
I know you say that you say that it's transported the right way up ..... but I don't see any way the oil can get in any other way, Unless you are driving like mad Max in an F1 car and the the G forces are forcing the oil up the crank case breather tube .

Could you please check that you are transporting the outboard with the tiller arm up, I've always found that counter intuitive, because the outboard is more stable tiller arm down.

The Service manual can be found here:
Google Search

I have electronic copies of both the users manual and the Service/Workshop manuals as .pdf's, but they are bit files 19 MB +.
PM me with your email address if you have problems down load them and I' try and forward them to you, but the link should work.

Thanks for that. I am certain that it was transported correctly. There is a sticker on it to warn me and in fact I sought out the manual, (downloaded from svb) in case this sticker had somehow been placed on the incorrect side,

To me, it is counter intuitive that the engine is meant to be carried with the oil filler and the carb on the low side...

Just checked, and definitely transported correctly

So the real question i suppose is what is the route for oil to get up into the cylinder and carb...

As I think about it, in the past the cylinder has been full of oil at times and required the plug to be removed, but not on this occasion.

I could kind of understand the cylinder filling via the rings and eventually into the carb? But the cylinder is not full now...

I have had other 4 stroke OBs in the past and never had this issue...

 

[Ian_Edwards]

There must be many Mercury/Mariner 2.5's around, and I've not see any other reports of engine oil getting into the Carb'. So it's either something that you are doing differently or a fault with your unit.
If the engine is running OK, then it's unlikely oil is getting in via the piston rings or the valve stems.
As i said the only other route is via the crank case breather.
Whether oil gets into the cylinder will depend on whether the inlet valve is open or not.
Are you overfilling the engine with oil?
I've found that the level you see in the sight glass is very dependant on whether the outboard is vertical. Any slight angle can make a big difference to the "reading".
You could try emptying all the oil out, then measuring the exact amount of oil required in the specification, and see where that reads on the sight glass.
Other than that I suggest that you take it to a dealer and get them to investigate.
After over 60years of owning, maintaining and repairing small outboard, I gave up 2 years ago and bought an ePropulsion electric outboard!
Since then I haven't had and outboard problem.

 

[pandos]

There must be many Mercury/Mariner 2.5's around, and I've not see any other reports of engine oil getting into the Carb'. So it's either something that you are doing differently or a fault with your unit.
If the engine is running OK, then it's unlikely oil is getting in via the piston rings or the valve stems.
As i said the only other route is via the crank case breather.
Whether oil gets into the cylinder will depend on whether the inlet valve is open or not.
Are you overfilling the engine with oil?
I've found that the level you see in the sight glass is very dependant on whether the outboard is vertical. Any slight angle can make a big difference to the "reading".
You could try emptying all the oil out, then measuring the exact amount of oil required in the specification, and see where that reads on the sight glass.
Other than that I suggest that you take it to a dealer and get them to investigate.
After over 60years of owning, maintaining and repairing small outboard, I gave up 2 years ago and bought an ePropulsion electric outboard!
Since then I haven't had and outboard problem.

Many thanks...I'll look at the crankcase breather, just in case the previous owner did something daft...

It never occurred to me that I had over filled it, I always guessed via the sight glass, but I'll measure in the correct amount and have a look...

..I have a honda air cooled in the shed and a Suzuki (which seems really light and nice to carry) but is in pieces (it came that way) so over the weekend I will solve my problems one way or the other