Danny:
I had a similar problem with my Spitfire 20 years ago! The first thing to do
would be to replace the fuel filter(s). I did not see that in your email.
Some Mk III's have a fuel filter near the tank which is often overlooked.
Most have a filter in the line near the pump, some have both, so check for an
aft filter. The fact that you just changed the pump leads me to consider
that the old pump may have failed as a result of having to suck too hard to
overcome a clogged or partially clogged filter.
In my case the problem was more difficult to track down. It turned out to be
a rusted vapo(u)r separator canister in the tank vent system. It caused a
vacuum to form in the tank causing it to eventually stall. After a few
minutes it would run fine until the vacuum built up again. First, open the
fuel filler cap, start the car and see if the car runs OK. If it does run OK
you have a tank vent problem. If it does not, you may have a different
problem, but maybe not. The vapor canister is located above the fuel tank.
If you enter through the boot (trunk for us Americans) and remove the
cardboard trunk liner, you can see it above the petrol tank. I just removed
mine and replaced it with a short length of metal tubing. You don't want to
leave the line disconnected as it will vent the fuel vapors from the tank
into the cockpit.
It could also be a problem with the charcoal canister as the tank vent line,
as does the float chamber vent, goes to the charcoal canister. (I had that
problem on the TR-6 several years back) Try removing the float chamber vent
hose and see how it runs. If it runs good you surly have faulty charcoal
canister. These theory's of course discount any internal problems in the
Carb itself. It seemed from your email that you thought this to be the case.
This should get you started in the right direction considering all of the
other things you have tried.
Best Regards,
Mark
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