1993 Johnson Evinrude "ET" 90 degrees CV Service Manual, P/N 508285, Page 286Get this manual
DRC3465
Shallow Water Drive Tilt Relief
1If the engine exceeds idle RPM while operating in shallow water drive mode (tilted up beyond the trim range), increased pressure beneath the tilt piston forces fluid through the tilt relief valve built into the manual release valve 2Fluid flows from below the tilt piston, through the tilt relief valveand to the reservoir3As the tilt piston moves down, the filter valve opens and allows fluid to flow from the reservoir to the top of the tilt cylinder4The motor will tilt down to the top of the trim range