Mercury 40 Service Manual page 246

TILT UP
In the up mode, as the trim ram (b) extends from the
cylinder, the memory piston (e) clears or uncovers
the pressure relief passage. Oil from the up cavity will
enter this passage and open the tilt pressure relief
valve (k). This valve lowers the amount of pressure
available to lift the outboard motor. With the engine
in forward gear, and at high engine rpm, the oil pres-
sure available will not be able to overcome the pro-
peller thrust, limiting the trim range to below the pres-
sure relief orifice. When the engine rpm's fall, or if
engine is not in forward gear, the oil pressure is avail-
able to extend the trim ram (b) up into the tilt range.
90-852572R1 JANUARY 1998 MID-SECTION - 5C-9