I have a '77 Merc 1750 with the old style round motor trim pump. It has the reverse lock solenoid. The reverse lock doesn't work. If I engage the reverse lock system by turning the valve fully clockwise like it should be, the trim doesn't work at all. The motor runs but doesn't trim the engine, so I have to run it with hte reverse lock disengaged. I was told by several people that I could replace it with a newer style oildyne unit for a mercruiser. I bought an Arco replacement pump. It replaces the oildyne pump directly. I installed it today and it lifted the motor fine but won't trim it down. If I run the pump long enough on down, it will trim the motor up????? Then I have to run it for quite a while on up for it to build pressure again to trim it up again. I understand that to trim it up, pressure must be applied to the lower end of the cylinders and to trim it down, pressure must be applied to the top of the cylinders. Correct? I am puzzled by the fact that both lines are going into the bottom of the cylinders. I checked both pumps and the new one pumps pressure out of one port on up and the other port on down. The old pump only pumps pressure on up, not down, so it seems that the motor is trimming down because of a lack of pressure on the bottom of the cylinders, not because of pressure on the tops of them. Can anyone explain to me how this system is supposed to work? <br />Any ideas as to how I can remedy my problems? I don't care which pump I use, but I would like to get one of them to work correctly.<br />Sorry this is so long, but I have tried to explain the problem in detail.
