The SU fuel pump is a fix before you install part if it has been sitting on
the shelf for a while. Over time on the shelf the rubber diaphram shrinks
generating too much resistance for the coil to pull enough to flip the
points over to push out the gas and start the process over again. The other
thing that goes wrong is that the points get corroded and need to be cleaned
up with a little emmory cloth and/or some contact cleaner depending on how
bad they are. Test the pump out using some wire to the positive and
grounding the body before you reinstall it. You may have to tap it to get it
started. Removing the nut on the positive post will allow you to remove the
plastic cap where the points are. You may have to untape the cap from the
coil body. If you run it without the cap installed make sure you don't lose
one of the pins that the points hindge on. Here is a repost of an earlier
post I made describing adjusting the diaphram and fixing the shrinking
problem....
Chris Reichle
creichle@nsc.msmail.miami.edu
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 pressurises 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
chamber.
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.
Chris
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From: mgs-owner
To: mgs
Subject: MGB fuel pump question
Date: Friday, October 17, 1997 8:48PM
Hello all,
A quick question regarding a dead fuel pump. I got stranded the
other day after the '68 B died. I determined that the fuel pump had broken
because no fuel came out of the line at the carbs when I turned on the
ignition and there was no audible clicking.
I ordered a new SU pump (negative ground) and installed it today.
It
doesn't work either. I checked the wiring and I get 12 volts ok. I tried
running the pump both with the out/in fuel lines connected and not. Neither
scenario resulted in the pump coming on. Am I right in assuming that even
if
there was a clogged line the pump should still start up when the key is
turned? Does this mean that both the old pump and the new one are broken?
Should I send it back and get a third?
TIA.
Steve
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schang@cis.ohio-state.edu | CIS Engineering
stchang@magnus.acs.ohio-state.edu | The Ohio State University
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