> I recently replaced the SU pump in my MGA (I think thats similar to the MGB
one 'cept that it is positve earth) The new pump primed itself in seconds
even
though there was scarcely any fuel in the tank.
Ian Gander
IGander@Mathsoft.com
I received a lot of replies telling me to switch my dead fuel pump from
the original SU type to one of the little solid state electronic ones. I
found them in J.C. Witney for $32. Probably good advice. But I have
decided I want to stay original, and I'm not going to give in to the SU
pump. (Does anybody else ever find themselves under their car, covered in
grease and oil, screaming, "You will work, damn it, you WILL work!" :-)
Anyway, resolved to get the pump to work, I bought a new set of points,
made myself a new cork gasket for the diaphram, and put the pump back in the
car. It now still runs continuously but pumps no fuel. I wondered whether
it was having trouble priming itself, since all of the fuel had drained out
of the intake line. I traced the line back to the fuel tank and started to
get puzzled. The connection from the tank comes out of the top of the fuel
tank's side. Now, why doesn't it come out of the bottom? How does the fuel
get out the top? There must be a tube inside the tank that comes from the
bottom and goes out the hole near the top. Anybody know?
Well, ignoring that issue for the moment, I measured the distance between
the highest point in the fuel line and the top of the gas tank. The fuel
line runs about 4 1/2 inches above the top of the tank. So the pump would
have to be able to raise the fuel at least that high when dry, in order to
prime itself. This is, of course, assuming the gas tank is full. If it's
less than full, the pump would need to raise the fuel higher.
I took the pump out and tested it using a battery charger for a power
supply. I screwed a bit of clear plastic tubing onto the intake port, stuck
it in a container of gas, and turned on the charger. The pump raised the
gas about 5 inches. Enough, it would seem, to prime the pump.
At the point I ran out of time and have yet to get back to the problem.
The way it looks to me a the moment: If I fill the gas tank totally full of
gas, the pump will have just enough power to prime itself, and everything
will work fine.
This does, however, raise a question in my mind. If this is the way its
supposed to be, then if you ever run out of gas in an MGB, you'd have to
completely fill the tank, you couldn't just fill up a few gallons to make it
to a gas station. That somehow doesn't sound right to me.
Anybody have any enlightening comments?
Jeremy DuBois
Programmer/System Administrator
Thermalogic Corporation
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