I have a 25hp 4 stroke '02 yamaha. Motor ran fine 1 weekend. The next weekend idled roughly, wouldn't go into gear without stalling. Replaced gas filter (cut open old one no trash or debris.) Pulled plugs they were black and and somwhat oily / gas smelling. Replaced plugs added sea foam gas treatment .5 pint : 6 gal. Engine ran about 20 min before fouling plugs. These are white scaley coated. Any ideas?<br />KC
