Listers,
I stumbled across something I thought I'd pass along. You may recall I've been
having trouble with the fuel pump in our
BN2/100M. I've got two pumps, one a 'factory' SU electronic, and one that came
with points that I retrofitted with an
SU electronic kit. Both pumps exhibit erratic behavior--sometimes behaving
like they should and sometimes pumping
quickly, then stopping, then pumping quickly, ad infinitem.
We've checked the lines--no leaks--and, suspecting a fracture in the tank
pickup tube, tried pumping directly from a
pail of gas. No change. Suspecting flooding, I installed Grose jets in the
carbs and, although any minor flooding
seems to be mostly controlled, the erratic pumping goes on.
What I found is, possibly, a good/better method for adjusting the diaphragm.
I've always adjusted them 'by the book;'
something like screw them in until the throwover mechanism just stops throwing
over, back off 4 'holes,' etc.; and (I
think) Rich C has suggested adjusting one hole looser than the book. The
electronic kit I retrofitted came with a
(fairly thick) feeler gauge, and I adjusted the pump per the instructions. The
pump sat unused for several years while
we started the restoration, and when the time came to install it it wouldn't
fire at all. In a hurry, I bought the
factory SU electronic and figured I'd revert the other to points for a spare.
In trying to solve our erratic pump behavior, I decided to give my retrofit
another shot. I didn't have the feeler
gauge, so I connected the pump up to a car battery and played with the
diaphragm adjustment. You'd expect that if the
diaphragm is set too tight the pump won't work properly, but I found that at
even one hole too loose the pump wouldn't
work either (this may be a 'duh' for some, but I've been working on these pumps
for years and it was a revelation for
me). There is about a 2-3 'hole' range where the pump will operate at all,
and one where the pump seems to work the best.
So ... my suggestion is when 'tuning' an SU pump--this should work for a points
pump as well--set the diaphragm per the
book, then connect to a 12V battery and set for the most robust pumping.
YMMV.
Bob
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Bob Spidell San Jose, CA bspidell@comcast.net
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