My MGB has been suffering from what seems to be fuel delivery problems, so I
just attempted this test. I attached a length of spare hose to the exit of
the fuel filter and ran it onto an open container (a measuring cup from the
kitchen). It was only a US pint container, so I didn't expect to be able to
run for a full minute.
When switched on, it started off fast, filling about 2/3 cup in less than 15
seconds. But then it stopped all by itself, so I switched off after 30
seconds.
If this is what it has been doing in operation, it would completely explain
the symptoms. After driving at freeway or expressway speed for a few miles,
the engine would sputter and lose power. After pulling over, I would hear
the fuel pump kick back in, and after a minute, I could accelerate away
smartly. In city traffic, it never had a problem, presumably because sitting
at idle at traffic lights would give the pump a chance to catch up.
This is a replacement SU pump from Moss that I only installed in late 2006.
Its predecessor failed in a similar manner, but only after at least 25 and
possibly 40 years.
--
Max Heim
'66 MGB GHN3L76149
If you're near Mountain View, CA,
it's the primer red one with chrome wires
on 12/17/09 4:50 AM, Paul Hunt at paul.hunt1@blueyonder.co.uk wrote:
> Assuming it's pretty much like the original MGB pump:
>
> If you have an SU pump then listening for clicking when turning on the
> ignition but before starting the engine is a perfectly valid test. Depending
> on how hot the engine was when last switched off it may click just a couple
> of times (cold) or for several seconds (hot). But if you turn the engine on
> within a few minutes of turning it off it may not click at all especially
> when cold. Note that some after-market types chatter all the time,
> regardless of engine demand.
> If it doesn't click at all after having left the ignition off for several
> hours or overnight then the pump or its electrical supply is probably
> faulty. If it clicks, then it should stop, and only make a single click once
> every 30 secs or longer. If it clicks more frequently than that then either
> the float valves are leaking and it will eventually overflow, which if you
> have a charcoal canister make take some time to appear on the ground, or the
> non-return valve in the pump inlet is leaking. If it continues to click
> rapidly then either you are out of fuel i.e the fuel level is below the
> pickup strainer, the pickup pipe is perforated above the fuel line, or a
> float valve or the non-return valve mentioned above are stuck open. If rapid
> clicking stops and starts while the ignition is on but the engine isn't
> running that implies either very marginal fuel level or the non-return valve
> intermittently sticking. Note that some after-market types output excess
> pressure which will overwhelm the float valves and cause flooding unless a
> fuel regulator limited to 2psi is also installed.
>
> If it clicks and stops as it should, then check delivery. Remove a fuel feed
> pipe from a carb (be aware it will spurt if the ignition has been on
> recently with SU and Moprod types), direct it into a container, and turn on
> the ignition. It should deliver at least one Imperial pint per minute, in
> practice closer to two, in a steady stream of pulses with minimal bubbles.
> Erratic pumping indicates pump or fuel level problems, lost of bubbles a
> leak on the tank side of the pump plumbing. Note that the delivery
> requirements apply to after-market types as well.
>
> If all that is right then the only other thing running the engine is going
> to tell you is if there is a very intermittent problem with the pump or its
> electrical supply that only being operated for a long time may reveal.
>
> ----- Original Message -----
>> What is the best way to check an original MGA fuel pump.
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