I have this piece of junk boat engine in my awsome boat.  It is a 2005 V6 Vortec with eldelbrock carb.  stickers on the engine say "ultra low emmissions engine."  Problem is when I shut the boat off it diesels or has run-on.  engine smells rich when I run it and has shitty gas mileage.  mixture screws are all capped..  any help!