Rob Becker wrote:
> Where is the cheapest place to get a new SU MGB Positive Ground
> Fuel Pump? Moss is quite expensive.. anyone have any ideas??
Well ... your cheapest alternative is to rebuild your existing
pump. Check for badly pitted points or a torn diaphram ... these
are the two bits that usually fail.
Remove the 'bakelite' cover and check the condition of the points.
Remove the six screws that hold the cast iron lump to the alloy base
... the diaphram is held in place between the cast iron lump and the
alloy base. Check condition of the diaphram.
The cast iron lump is a coil (electro-magnet) ... the diaphram has a
lump of iron and a shaft attached to the coil side ... note the
spring that is fitted over the shaft and that the other end of the
shaft is connected ot the points. When the coil is energized (the
points are closed) it generates a magnetic field that pulls the iron
lump/diaphram upward, drawing fuel into the pump, until the shaft
opens the points ... when the points open, the magnetic field
collapses and the spring forces the diaphram downward pushing fuel
out of the pump and closing the points. This cycle continues until
adequate pressure is build up in the line (3-4psi) to prevent the
spring from forcing the diaghram downward.
When the magnetic field collapses it generates a voltage spike that
arcs across the points ... it is this arcing that pits the points.
Initially a capacitor was fitted to reduce the arcing and increase the
life of the points ... this was replaced by a condensor, and then
finally a zener diode ... each have greater success. Check the
following url on how to add a transistor and diode (in lieu of either
the capacitor, condensor, or zener diode) to 'do the coil switching
work, so the points last indefinitely' ...
http://www.jag-lovers.org/books/old-xj6/SU_fuel_pump.html
The coil and points are not sensitive to polarity ... however, the
bits that have been fitted to reduce the arcing are sensitive to
polarity (the condensor, zener diode, and/or tranistor).
A rebuild kit is available from Burlen Fuel Systems (Joe Curtto, Moss,
VB) at a modest cost ... it includes the seals, diaphram, points, and
zener diode. The procedure for properly fitting the points and diaphram
are outlined the workshop manual.
Oh ... 'I ain't dat smart' ... thanks to Barney/Dan for helping understand
the function of the coil/zener diode, and to Bill Eastman for the url.
Now if I could just figure out how to identify the transistor's emitter,
base, and collector ...
Safety Fast! ... larry.g.unger@lmco.com
'61 MGA 1600 MkII
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