1985 OMC 65, 100 and 155 HP Models Commercial Service Manual, PN 507450-D, Page 70Get this manual
155 Model
1Connect throttle shaft amplifier shown, to the top carburetor throttle shaft,
such as the one
2While rotating the throttle cam, the first embossed mark on the cam that contacts the cam roller should align with the center of the cam roller as tip of the amplifier begins to move
3To adjust, align the embossed mark on the throttle cam with center of the cam roller, loosen the carburetor cam roller screwAllow the throttle spring to close the throttle valvesWhile pressing on the cam follower lever hold the cam roller against mark on the throttle cam and tighten the screwRecheck that the throttle valves begin to rotate as the embossed mark aligns with center of the cam roller4Connect timing light to No1 cylinder spark plug high tension lead5Advance the throttle by moving the throttle lever until tip of the amplifier begins to moveRemove the amplifier but do not move the throttle leverOn some models the idle stop adjustment screw may be advanced until center of roller aligns with first mark on camAfter timing is checked return idle adjustment screw to original position6Start the engine and observe spark advance with timing lightThe proper spark advance is listed below