1988 mercury 75 4 cyl fuel pump, serial - 6558668

[kgrovesyboy]

Hi everyone, hope someone can help me,
I have a 1988 mercury 75hp 4 cylinder outboard, I haven't used it in the water yet (too cold here)
but, it always takes a while to start and just recently it has been bogging down while on idle for around 30 seconds.
it seems to be fuel starvation so I thought id check the fuel pump out (triangular type). but it doesn't pump any fuel.
ive taken it apart, diaphragm seems ok, but I seem to be missing a spring and cup type piece that is shown on the fuel pump diagram I have. looks to me that this spring pushes the diaphragm forwards.
ive done a compression test on all cylinders, all 150psi, im wondering if its the case that someone's had the pump apart before and missed some bits out, just wondered if anyone has rebuilt one of these and knows if the spring and cup type part is required,
thanks
kev

 

[carholme]

Re: 1988 mercury 75 4 cyl fuel pump, serial - 6558668

That s/n comes up as:

MERCURY - ( 75 H.P. (1984 )) Note 1984 not 1988
Serial No: 06558668 Model No: 1075624

Parts List for model 1075624:

75 H.P. - Mercury, Mercruiser, Force, etc. Parts Lookup

If you are talking about items 6/7 in this link, yes, they are required.

Mercury, Mercruiser, Force, etc. - FUEL PUMP AND FUEL LINES (TRIANGLE FUEL PUMP) - 75 H.P.

FUEL PUMP. Diaphragm type fuel
pump is used. Fuel pump is actuated by
crankcase pulsations. Early models are
equipped with "triangle" shaped fuel
pumps. Later models are equipped with
"square" shaped pumps.
Fuel pressure on early "triangle"
shaped pumps should be 2 psi (13.8 kPa)
minimum with motor running at full
throttle. Fuel pressure on later
"square" shaped pumps should be 2 psi
(13.8 kPa) at idle speed and 5.5-6.5 psi
(37.9-44.8 kPa) at full throttle.
Renew gaskets and diaphragms whenever
fuel pump is disassembled. On early
"triangle" shaped pumps, install
check valve retainer with tips of retainer
pointing away from check valves. Be
sure check valves are installed into the
correct bore. On some models, check
valves are color-coded red and white.
Red check valve must be installed into
intake side of pump.
On "square" shaped pumps, install
check valves as shown in Fig. M12-33.
After installing check valve retainers
(4), cut retainer off at ridge to prevent
contacting pump diaphragm.

Gerry