What makes a 4 stroke smoke?

Boat of Us 2

Cadet
Joined
Nov 23, 2006
Messages
8
I own a Mercury 90hp 4 stroke 2004.
It has less than 100 hrs.

I recently changed the spark plugs and noticed one had abit of oil on it. I also noticed that it smokes alot from the exhaust which is definatly not normal for a 4 stroke.

Does anyone know what's going on. I'm abit discouraged...

Thanks..
 

Chris1956

Supreme Mariner
Joined
Mar 25, 2004
Messages
27,035
Re: What makes a 4 stroke smoke?

4 cycle motors should not smoke at all. Is there some residual fuel stabilizer from last winter in the gas? Did someone put some oil in the gas?

Try a fresh remote tank of gas. if that doen't clear it up,you may have some issues with rings, head gasket, valve guides or something.
 

Boat of Us 2

Cadet
Joined
Nov 23, 2006
Messages
8
Re: What makes a 4 stroke smoke?

Thanks for your reply...

Can it be the seals that are dried up because I don't run the engine often?
 

Chris1956

Supreme Mariner
Joined
Mar 25, 2004
Messages
27,035
Re: What makes a 4 stroke smoke?

I am not too familar with 4 cycle outboards, so I cannot comment on the "seals" theory you have, however, it sounds unlikely.

I have noticed that 4 Cycle Sterndrive motors (i.e. Small Block Chevy) tend to smoke a bit when first started. perhaps some oil slips past the valve guides into the combustion chamber, while they sit between runs. Maybe you have the same thing?
 

whyboats?

Cadet
Joined
Jul 17, 2009
Messages
14
Re: What makes a 4 stroke smoke?

not familiar with 4 stroke outboards but the valve seals can dry up on an inboard motor causing oil to slip into the cylinder between the stem of the valves and the valve guides. this is pretty much what chris1956 said but I wasn't sure if you knew that there are seals that can be replaced.
 

CharlieB

Vice Admiral
Joined
Apr 10, 2007
Messages
5,617
Re: What makes a 4 stroke smoke?

Have you checked your oil lately?

Is it OVER-FILLED?

If the fuel pump diaphragm is leaking it will fill the crankcase with fuel causing the fuel/oil mixture to blow out the engine breather into the carb intake and the burning oil in the cyl makes smoke.

Pontoon boats with the fuel tank higher than the carb can also flood, gravity flow (siphon) fuel thru the carb, floding the intake, leak past the rings and fill the crankcase.

If the engine oil is higher than normal then start finding out why.
 
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