1971 Johnson 125HP outboards Service Manual, Page 68Get this manual
DESCRIPTION
EXHAUST HOUSINGS The lower writ features "wet sleeve" exhaust system consisting of an inner and an outer housing with water chamber in betweenThe water discharged from the engine cooling system fills the space between the exhaust housings and maintains specified level when the engine is runningSee Figure 6-1The water drains out when the engine is stoppedThis chamber of water serves as an effective silencer, quiets the exhaust relief, and cools the outer housing and lower rubber mountExhaust gases are discharged underwater through the propeller hub for efficient SilenCing and performanceWater inlets in the trim tab scoop up water and direct it back into the exhaust chamber to cool exhaust gases through the propellerEXHAUST RELIEF Normally, exhaust gases are conducted down through the inner exhaust tube and out through the underwater exhaust outletHowever, in starting, water in the underwater outlet creates back pressureThis can cause hard startingExhaust relief is provided by an outlet passage above the waterlineThe exhaust gases will initially be discharged through the exhaust relief outletSee Figure 6-1RUBBER MOUNTS The outboard isolation system consists of pair of tough tubular mounts with rubber bushings designed and located for efficiencySee Figure 6-1In addition, the motor covers are rubber isolated from the power head and exhaust housing adapterSHOCK ABSORBERS Two hydraulic shock absorbers are mounted between the swivel bracket and stern bracket to reduce the shock resulting from hitting an underwater obstruction at high speedCOOLING SYSTEM The cooling system is pressurized, reCirculating, temperature-controlled systemThe thermostat maintains consistent operating temperatures throughout the entire range of motor operation, increasing motor life and efficiencySee Figure 6-1SPRING