I recently bought this motor and had it tuned and a new water pump installed by a local marina. It is a 1968 Evinrude 55 hp Triumph. Took it out yesterday and it runs smooth through the whole throttle range; however, if you run it at half throttle for any length of time (a minute or so), it looses power and the speed drops considerably, still running pretty smooth. I believe one of the cylinders cuts out. If you throttle up to 3/4 or full and let it run there for a minute or so, it will surge a few times, and then take right off. Alternately, if you simply shut the motor off, when you restart it, it is fine. We tried squeezing the primer bulb while it was acting up. The bulb was hard and seemed to make no difference, so I don't think it is fuel pump. Any help would be greatly appreciated. The mechanic at the marina can't come up with anything concrete, and I can't afford for the marina to be guessing at shop rate. Thanks.
