[Healeys] SU fuel pump adjustment

Bob Spidell bspidell at comcast.net
Sun Sep 26 09:53:01 MDT 2010


  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 at comcast.net

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