> Can you elaborate on this? I have a couple of SU pumps from A's that
> are worth rebuilding and I'd like to know the reasoning behind adding
> the capacitor/diode and how it is done.
The capacitor was included in the rebuilt kit I bought. The principle
of operation and placement is identical (in parallel with the points)
to the condenser protecting your car's points from burning out (ie. it
provides an alternative path for current flow as the points are separated
and helps prevent the formation of an arc).
The diode is used on most new SU pumps. It is connected in series with the
pump coil and its job is to "short-out" back emf generated by the collapsing
magnetic field when the points are opened.
The diode is what makes new su fuel pumps either positive or negative
ground. So buy the cheaper negative ground and flop the diode.
Either of these measures are very effective at reducing arcing and will
greatly increase the life of SU pump points. Like the points in your
ignition system, SU pump points will wear out and have to be
replaced. As you are all aware, British cars were designed for
frequent regular maintenance. A good solution to eliminating the
points is to fit an electronic optical switch (I believe there is an
Australian kit to do this).
The next thing to make sure you get right when you install a _new_ diaphragm
is the pump throw over. Here is the procedure as outlined in the Healey
work shop manual:
Holding the coil housing assembly in a approximate horizontal position,
push the diaphragm spindle in, firmly but steadily. Unscrew the diaphragm,
pressing and releasing with the thumb until the rocker just "throws over".
Now turn the diaphragm back (unscrew) to the nearest hole and again 4
holes (2/3 of a complete turn). The diaphragm is now correctly set.
How many of you SU bashers have done this procedure before :-?
Other things to check:
- one way valves .. replace them from the kit. If you have an earlier
pump with built in valves contact me and I'll tell you how I cleaned
up the seats on my pump.
- point wiping - set the points up so that they correctly wipe against
each other.
- filter and tanks. There is a filter in the pump and there should be
a screen in the tank. How many of you have marginal rusted and
plugged tanks and lines? Do a flow and pressure test ...
- add a clear fuel filter immediately before your carbs. Not only does
this catch crud from you pump rebuild :-) it lets you see at a glance
if lack of fuel is the reason for a no start..
- many more that I can't think of right now ...
--rod.
ps. SU carbs are happiest when their fuel is delivered by SU pumps.
--
Rod Barman, Dept. of E.E., University of British Columbia
rodb@ee.ubc.ca
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