Mercury Optimax 115 Service Manual page 142

REF. REF.
QTY.
NO.
1 1 FUEL PUMP ASSEMBLY
2 2 DIAPHRAGM KIT
3 1 DIAPHRAGM
4 2 RUBBER CHECK VALVE
5 2 RETAINER
6 1 SPRING
7 1 CAP
8 1 SPRING
9 1 CAP
10 1 DIAPHRAGM
11 1 GASKET
12 1 GASKET–boost
13 1 GASKET–pulse
14 1 PLATE
15 2 FITTING
2 SCREW–fuel pump (M5 x 40)
16 16
2 SCREW–pump to crankcase (M6 x 50)
17 1 BASE
18 1 ELBOW (45 Degrees)
19 1 FITTING
20 1 TUBING (6 IN.)
21 5 STA STRAP
22 1 HOSE (W/Insulating Sleeve) (7 in.)(177.8 mm)
23 1 HOSE (W/Insulating Sleeve) (18 in.)(457.2 mm)
24 1 CONNECTOR
25 1 CLAMP
Fuel Pump Description/Operation
The fuel pump is a crankcase-pressure-operated, diaphragm-type pump. Crankcase pul-
sating pressure (created by the up-and-down movement of piston) is transferred to fuel
pump by way of a passage (hole) between crankcase and fuel pump.
When piston is in an upward motion, a vacuum is created in the crankcase, thus pulling
in a fuel/air mixture [from Vapor Separator Tank (VST)] into crankcase. This vacuum also
pulls in on the fuel pump diaphragm, thus the inlet check valve (in fuel pump) is opened
and fuel (from fuel tank) is drawn into fuel pump.
Downward motion of the piston forces the fuel/air mixture out of the crankcase into the
cylinder. This motion also forces out on the fuel pump diaphragm, which, in turn, closes
the inlet check valve (to keep fuel from returning to fuel tank) and opens the outlet check
valve, thus forcing fuel to the VST.
90-855347R1 JANUARY 1999
DESCRIPTION
FUEL PUMP
Fuel Pump
TORQUE
lb-in lb-ft Nm.
55 6
55 6
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