Honda BF2D Burning Smell

[pporesky]

I have a 2003 Honda BF2D 2HP outboard used on our dinghy. Engine has always run great. This weekend I noticed a very noticeable burning smell and smoke when the engine is revving at high RPMs.

Odor and smoke disappear at low RPMs.

Andy suggestions on where to begin troubleshooting?

[Cptken]

odors and smoke in the exhaust or from under the cowling?

If exhaust is your fuel mixed properly?

If under cowling, pull it off and look. Is the telltale pissing water? Is the water pickup fouled?

Didn't give us much to go on....any other information?

[MarkSF]

That's an air-cooled design I believe.

[PaulinVictoria]

Air cooled and 4-stroke. What colour is the smoke? It is under throttle/load or when you back it off?

[dabnis]

The water pump cools the exhaust passage after it leaves the head.
Perhaps the impeller is going bad or there is debris in the pickup?
I have the same engine and have picked up plastic bag material.
Odor and smoke ? maybe the crankcase is over filled, it doesn't
hold much oil, the dipstick should tell.

Dabnis

[pporesky]

This is a four stroke, air cooled motor so there is no water/pumps/impellers that I am aware of and no fuel mixing.

Smoke comes from the top of the unit out the back air vents and was light colored. The smoke was limited as I would quickly back off the throttle when the burning odor became obvious.

At very low RPMs the burning goes away and is repeatable.

One other symptom is that a small amount of oil appears appears to be leaking out from somewhere (but not the oil drain plug) as I notice that the bottom of the engine case is unusually dirty and oily. And the amount of oil in the reservoir remains at normal levels.

[dabnis]

My engine is an 1986 model and pumps water through the lower
unit exhaust passage to cool it, but the upper engine block is air cooled.

http://marine.honda.com/pdf/manuals/31ZV0610.pdf

See page 15 & 37

Not sure about the newer models although the 2002 Manual says
to "Flush it" after using it in salt or dirty water?

Sounds like perhaps oil is leaking from somewhere on the engine,
maybe a leaking gasket? Maybe if the engine is tired it has excessive
blow by causing oil to leak past the seals or gasket joints?

Dabnis

[pporesky]

I read the manual you posted and the 2003 model is different. There is no water intake and no check hole to cool the lower exhaust unit.

To winterize the unit each year I perform all maintenance with it completely out of the water and to date this has caused no issues so I hope there is no dependence on water cooling.

I have used the unit each weekend and this past Sunday on one of the trips to the dock is when I first noticed the smoke and burning smell. It was obvious. I have been noticing the small oil leak all season and thought it was related to putting too much oil in the engine this winter. But I have since taken some out and the burning has just started to occur. How can I check to determine if a leaky gasket is a culrprit?

The overall condition is good and I consider the amount of usage to be average as I probably only go through a few gallons of gas per year for the past eight years. This is the first known issue I have had with the engine.

[dabnis]

Only thing I can think of is to completely clean the entire outside
of the engine and watch where it starts to leak after cleaning.

Dabnis

[pporesky]

One other question on a related note:

Where is the idle adjustment screw on these engines? I see the two nuts under the gas tank but this seems hard to reach/adjust.