1980 Johnson 2HP Service Manual, Page 43Get this manual
EXHAUST 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 pressure and hard startingExhaust relief is provided another outlet located in the water discharge passage above the water lineSince water is discharged until after the motor is started, the exhaust gases will initially discharged through the water outletSee Figure 6-1WATER PUMP
EXHAUST RELIEF HOLES
Figure 6-1Exhaust Relief and Swivel Bracket Screws
HIGH SPEED LOWSPEED
Water for cooling the powerhead is circulated the water 10cated at the top of the gearcase and driven directly the driveshaftThe consists of synthetic rubber impeller which is keyed to the driveshaft, and the housing which is offset from the center with respect to the driveshaftBecause the housing is offset, the impeller blades flex as they rotate, varying the space between themThe inlet port, located in the lower part of the housing, is open to the blades when the space between them is increasingThe outlet port, in the impeller housing, is open to the b1ades when the space tween them is decreasingThus the impeller works as displacement See Figure 6-2Water is conducted from the in the lower unit to the powerhead through copper tube in the exhaust housingAt higher speeds, water resistance keeps the b1ades from contact with the housing and the acts as centrifugal Water is conducted from the in the lower unit to th powerhead through copper tube in the exhaust housingSee Figure 6-2