I have an 90hp 1985 evinrude with a 13 3/4 15 prop carbs rebuilt last season about 20hrs on them on a 1984 170 tourney grady white hull everything runs fine wot rpm runs about 4500 to 4800 at about 23 to 26 mph BUT every so often it will jump up to 5000 to 5400 rpm and the boat speed jumps as...