Paul Gilders (also on the list here, but currently out of town) has a
1976 MGB that has an odd problem. He went out of town for about two
weeks, and I had the car. It sat for about one week and left its mark
with about a gallon of petrol on the ground. I think it was trying to
tell me that it was going to use fuel one way or another, and I would
have to drive it to stop the leak. :-)
Paul stopped back in town and we decided to see if we could get the
car to relieve itself in the proper manner. After much searching for
this fuel leak, we traced it to somewhere around the charcoal
canister. It was likely that the fuel vapor recovery system had
petrol and not vapor in it. So, we blew a bit of air through the fuel
vapor line leading to the top of the gas tank. That pushed some
petrol back into the tank as well as making some air bubbles in the
tank. Note that the gas tank was 1/2 full. "Bubbles? It's not
supposed to make bubbles!" That meant that vacuum was pulling petrol
(not vapor) into the vacuum system of the car, and when the car was
shut off, the anti-run-on valve would open and dump petrol on the
ground! Blowing into the charcoal canister proved this when a pint of
gas was dumped onto the ground. Since the hose from the anti-run-on
valve is lower than the tank, it would sometimes siphon out even more
petrol.
Why would we be able to blow bubbles into the top of the fuel tank?
>From the Haynes manual something like this should exist in the tank...
Fuel vapor line connection
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\__________________________/
Note that this is a brand new gas tank just installed a few weeks ago.
It's my guess that this tank is missing the right half of the vapor
connection inside the tank, and just has a straight tube that goes
down inside the tank. We also could draw petrol from the fuel vapor
connection with a syringe and a tube. Our fix for now, was to remove
the vapor vacuum line from the charcoal canister and plug the vacuum
lines. We had some concern as to how the gas tank would vent, so we
removed the rubber stopper from the cap so that air could enter the
tank as fuel was burned.
When Paul get's back into town we'll give the place that sold us the
tank a call, but I thought I would tap the knowledge from the list as
well. Assuming that we can't get another tank, what should we do?
I'm think that we could tap the filler pipe and connect the vapor line
there if need be. Other ideas? Anyway, it was an interesting problem
to track down.
---
"Well, if you can't believe what you read in a comic book, what *can*
you believe?!" -- Bullwinkle J. Moose [Jay Ward]
-Scott
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