Mercury Mariner Outboard 225 3 Litre Service Manual 1994, Page 70Get this manual
Idle Speed Adjustment 1With engine in water, connect fuel line to engineStart engine and allow to warm upIf belt tension is not correct, loosen pivot bolt and tension adjustment boltMove alternator away from fly wheel to increase tensionTighten tension adjustment bolt [Torque to 40 lbft(54.2 Nm)] and pivot bolt [Torque to 40 lbft(54.2 Nm)]2
Place outboard in gear and monitor engine RPMIf RPM is above or below recommended RPM
(550-625), verify carburetor synchronization is correct
andor readjust idle mixture screwsIf necessary,
Throttle Position Indicator lock screws may be loosened and TPI readjusted to attain recommended engine speedA 0.05 volt change in TPI setting results in degree change in timingRetighten TPI screws
NOTE: belt tensioning tool (obtain locally) may also be used to adjust bell tensionAdjust belt tension to 60 lb (355.8 N)
a TPI Screws