1975 Evinrude 40 HP Outboards Service Manual, PN 5093, Page 42Get 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 functioning, check
operating in neutral, crankcase suction may become abnormally highThis high suction (vacuum) will cause erratic functioning of the carburetor, allowing the motor speed to increaseThe function of the cut-out switch is to short out the breaker point for the lower cylinder momentarily when crankcase suction increases, preventing the bottom spark plug from firing and thus reducing motor speedThe safety switch completes the cut-out switch circuit and prevents it from operating at full throttleThe safety switch should be adjusted on its bracket so that it opens the circuit when the plunger is at the mid-point on the slope of the shifter lock stopSee Figure -3 7An ohmmeter or test light should indicate closed circuit when the plunger is below the cam slope
the manifold vacuum hose for leaksCheck the hole in the intake manifold with #76 drill to make sure that it is not cloggedCheck 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 switch, vacuum hose connector will indicate switch operationTest light should light under suction and not light under pressureSee Figure 4-38If switch operation is faulty or erratic, disassemble the cutout switch and inspect the diaphragm and contactsReplace parts as required and reassemble See Figure 4-39