I bought a 97' Sun Tracker 25' pontoon boat with the original 97' "Tracker by Mercury" 75 hp O/B 2stroke(-). The motor seems to run okay, but fuel consumption seems high to me. (1) Is this really a Mercury motor or an offbrand- make? (2) What fuel economy should I expect? (3) How fast should a 75 hp push this big pontoon at WOT? (4) It was idling rough, so I replaced the 3 plugs, which showed a lot of oil fouling -- Is this normal for this 2stroke-? (5) Occasionally it backfires slightly when re-starting cold -- What could cause this? (6) The tachometer is wildly erratic -- is this likely just a defective tach, or is this a defective engine sender? Sorry to blast you guys with all these dumb questions, but I'm' new to outboards!