1971 Evinrude 40HP outboards Service Manual, Page 56Get this manual
DESCRIPTION RUBBER MOUNTS The exhaust housing assembly, which carries the power headfloats on the steering bracket and pilot shaft assembly on six rubber mounts and two rubber bumpers In this way, all 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 is provided by another outlet located in the water discharge 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 outletE HAUST HOUSING BUSHING, HOUS TO CRANKCASE
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SLOW SPEED