Mercury Mariner V-250 V-275 Outboard Service Shop Manual 1990, Page 319Get this manual
Throttle Cable Installation and Adjustment to Engine "'CAUTION
Engine Idle MUST NEVER EXCEED 800 RPM In gear1Start engine and adjust engine RPM to 650-700 RPM in forward gear
IMPORTANT: Excessive preload on throttle cable will cause difficulty when shifting from forward to neutral (Readjust throttle cable barrelif necessary