Our houseboat was powered by a 90 HP 1984 Evinrude. The powerhead went recently (badly scored cylinder walls and piting/burning of cylinder head) Just prior to this, the engine would hesitate (balk) at high speed.It would run at high, then rpm would reduce. I inspected all fuel lines, cleaned filters. Also have a glass water separator in the line. I cleaned this . . All to no avail. I was told that it was probably bad fuel and/or water in the fuel).<br /><br />I pulled some fuel from the bottom of the tank (I have a bottom drain for such a purpose) and noted no water. Also put dry gas in tank.<br /><br />Well, the 90 hp finally died as describe above. We replaced it with a 150 hp 1984 Evinrude. A very clean engine, Carbs rebuilt, good compression, etc. Well, the engine was installed, tested statically without the houseboat moving. Took the houseboat out for the first time last evening and lo and behold . . .same problem!!! At first the engine was perfect. THen, within about 10 minutes, rpms began to fall and it would sometimes leap to full for a few seconds then drop back. If engine was stopped and restarted, it would go to full throttle, but then fall back and surge.<br /><br />1. What could be the cause?<br /><br />2. If it is bad fuel, could running the engine with bad fuel cause scoring of the cylinders/the demise of the prior engine!!!<br /><br />(The fuel in the tank was fresh and did have Stabil in it)
