I have a 20 ft suntracker pontoon with a 50 hp merc 2 stroke on it. Never had a second of trouble out of it in the 2 years i haveowned it. Last time i ran it was thanksgiving weekend of 2011. Got it out the other day hooked the hose up and within 5 seconds of turning over it busted off fine. Revs up good and idles perfect. Went to put it in the water yesterday and it cranks fine but when i got out to the channel and gunned it, it went up to about 4000 rpm and then bogged down and shut off. IT did this several times and i was never able to get more than 4200 rpm out of it without it bogging and stalling. It will cruise around at 3000 rpms and idle fine. Any help wold be appreciated. Also we always use staybill or however you spell it in our fuel and usually put mid grade fuel. Last time i filled up i did it at a station that serves non-ethanol fuel. But it was probably mixed with a half a tank of 10% ethanol fuel.