I know what this is thatnks to the help of fellow list members. I too went
through SU fuel pumps until someone tipped me off to the adjustment of the
diaphram post that connects to the sping plate thingy ( good description I
This is the deal. Someone told me ( sorry for not giving proper credit )
that the diaphram adjustment is sometimes not done properly when they are
assembled or in my case, the rubber shrinks and the diaphram is too taught.
When the diaphram is pulled up to suck gas into the chamber, the post (which
looks like a long nail with a threaded end) flips the points to the off
position. When you look at the points you will notice that they are spring
loaded and snap closed and open. The problem in my case was that the
diaphram was too tight and would not allow the post to be pulled up high
enough to flip the points to the off position. Normally,once in the off
position the post is released by the coil and the diaphram presurises the
gas pumping it through the valves. When the diaphram is at it's lowest
position, it snaps the points back to on and more gas is drawn into the
In my case, I removed the pump and unscrewed it with the intentions of
rotating the diaphram one hole to the left to adjust the post so that it
would come up high enough to flip the points to off. What I found when I
opened it was that the diaphram was really tight and just didn't have the
range of motion to both flip the points off and on. It was still stuck to
the coil side of the pump so I was able to try to actuate it manually. I
peeled the diaphram off and then (leaving it in the same position) screwed
it back togather and have not had a problem since. Peeling it off allowed
the diaphram to realign on the screw holes normally, not being stretched.
Either you have to adjust it by rotating the diaphram or it may be just too
tight like mine was. I bet I could have said this all in about 4 sentences.
Sorry about the length for all of you that made it this far.
To: MG Mailing List
Subject: Fuel Pump Failure (again!)
Date: Thursday,January 11,1996 9:27AM
I have had a second fuel pump go out in as many months on my '73 MGB.
The SU brand pump failed by becoming totally silent. This one (a
plastic-bodied one from Seven) will click once for voltage applied, and
once when it is removed. It doesn't "throw over" though. I got home
yesterday by clicking the ignition on-off to fill the float bowls (5
miles, in traffic. Yeesh). The SU responded to tapping for a while
before it completely died. This one doesn't, and I am afraid to hit it
too hard because of the plastic, anyway.
This is starting to look chronic! Any ideas? Thanks!
John M. Trindle | email@example.com | Tidewater Sports Car Club
'73 MGB DSP | '69 Spitfire E Stock | '88 RX-7 C Stock
Home Page: http://www.widomaker.com/~trindle
"I believe in computer dating, but only if the
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