I wonder about the "paint" you said you saw in the fuel lump bowl. Ive had two boats over the last few years. One was a carbed mercruiser, other was an multi port fuel injected indmar. Both were pre 2002 models and had ethanol fuel issues. Rubber sheets came from the rubber fuel hose and would clog, black particles and rust particals would clog everything. Ive had to rebuild the carb, all fuel injectors, fuel rails, replace hoses and filters on both boats to get them back right. My carbed boat had to also have accelorator pump and linkage replaced and adjusted to provide a good throttle response. Just some ideas that might help you on your way.