1974 Johnson 40 HP Outboard Motors Service manual, Page 41Get this manual
VACUUM CUT-OUT AND SAFETY SWITCHES If the throttle is suddenly closed while the motor Is
If the vacuum cut-out switch is not fun tioningheck
operating in neutral, crankcase suc tion may become abnormally highThis high suction (va cuum) will cause erratic funCti oning of the carburetor allowing the motor speed to inc reaseThe fun ction of the
cut- out switch is to short out the breaker point for
the lower cylinder momentarily when rankcase suc tion inc reasespreventing the bottom spark plug from firin and thus reduc ing moto speedThe sarety switch ompletes the cut- out switch circuit and prevents it from operating at fulllhrotUeThe safety switch should be adjusted on its bracket
the manifold vac uum hos for leaks, and heck the ho le in the intake manifold with76 drill to make sure that it Is not clogged and check for wire continuity (see Section 3) To check the operation of the cut-out Switch, connect test light to the switch terminal and to groundAlternate suction and pressure at the witch vacuum hos connector will indi cate switch operationTest light should light under uction and not light under pressure See Figur 4-38If witch operation Is faulty or erraticdi sassemble the cut-out switch and ins pect the diaphragm and contacts Replace parts as required and reas mbleSee Figure 4-39