Short recap: I've been chasing a low rpm problem with this engine; only able to get 3700 rpm with a 14.5 x 17 prop. Yesterday I put on a 16 x 13 prop, and low a behold, 5600 rpm! Ran all day long, not too hard, but tested it here and there and trolled a lot. Then, about 5 hours into the day, the...