carboned plugs

[cariocaone]

I have two 115 4 strokes with aprx 760 hrs. Stbd engine = perfect. Port eng = ongoing intermitent starting problems, but only after 4 plus hrs of operation. engine will restart after cooling down, but the problem seems to occur after idling for several min. after mid to higher rpm crusing. I put new fuel filters,changed plugs and checked resistance of coils/wire harness. 20+ hrs after service, plugs carbon up... Any ideas??? ( ps motors are 2005)

[boats.net]

Start by running compression and leak down test, post results.