1971 Johnson 40HP outboards Service Manual, Page 56Get this manual
DESCRIPTION
RUBBER MOUNTS The exhaust housing assembly, which carries the power head, floats on the steering bracket and pilot shaft assembly on six rubber mounts and two rubber bumpersIn this wayall power head and driveshaft vibrations are isolated and prevented from being transmitted to the stern bracket and boat transomSee Figure 6-1EXHAUST RELIEF Normally, exhaust gases are conducted down through the exhaust housing and out the underwater outlet in the gearcaseThe siphoning action of the propeller and water provides an unrestricted escape for exhaustHowever, in starting, water in the outlet creates back pressureExhaust relief isprovided by another outlet located in the waterdischarge passage above the water lineSince no water is discharged until after the motor is started, the exhaust gases will initially be discharged through the water outletEXHAUST HOUSING BUSHING, HOUSTO CRANKCASE
IMPELLER AT
SLOW SPEED