Black Spark plugs?

Question

With clean spark plugs my mercruiser boat engine is fine but they soon clog with black dry soot like deposits and the engine is then very difficult to start. I suspect it's something to do with fuel but what?

Answer 1

carbs need fine tuning

Answer 2

dont touch the carb til youve changed the air filter

Answer 3

Definitely fuel mixture problem. Or it can be poor ignition who causes the plugs to fail so fast.

Do your engine is a 2 strokes ? Then too much oil in the fuel will soot the plugs fast also.

Answer 4

It;'s carburretor check-up time since it's running really rich, and just off-the-cuff, it sounds like you've perhaps got the choke stuck on.

Answer 5

Far too rich a mixture or,oil is getting into the cylinder/s

Answer 6

running rich...done any maintenance recently?

possible cause:  carb float height needs adjustment, or worn float needle & seat

Answer 7

Your right.  Carbon is caused by the engine running too rich.  That can be from the float setting too high or if the choke flapper or secondary are sticking.  With the engine hot and running.  Take the flame arrester off the carb.  Then with someone else driving the boat, bring it to full throttle.  As the boat accelerates both air plates should open fully, so that you can look directly into the venturi and see the fuel being sucked into the engine.  The throttle plates should be at 90 degrees.

Answer 8

You are right. It is a fuel problem. The gas mixture is way too rich. Try getting the carburator adjusted.

Answer 9

black deposits on the spark plugs suggests an over fuelling problem adjust the carburetor or get the ECU checked if its fitted with an ECU or it could be the fual injectors try a fuel system cleaner and give the engine a good hard run to clear out the system, also try a carburetor/throttle body cleaning spray

hope this helps