Walt,
The simple solution to the pressurised tank problem is to cut away part
of the gasket on the cap so that the tank vents. Immediate problem will
be solved, but the underlying problem remains.
The fuel system is set up so that vapors and pressure from the tank
vent up into the round can inside the right rear fender, then the vent
tube continues forward to the engine space and eventually hooks up to the
black, cylindrical, charcoal cannister. That, in turn, is connected to
the suction side of the engine and to the great outdoors. Vapors and any
liquid go to the can in the fender, vapors separate there and keep on
going to the cannister, where they are adsorbed onto the charcoal and
held. Then, when the engine starts, the low pressure of the engine sucks
in the vapors, they get burned and evaporated gas does not go to the
atmosphere.
So, when you have pressure building up in the fuel tank, the underlying
cause is that there is an obstruction in the venting system somewhere.
It can happen that the pressure builds up to the extent that gas is
pushed past the float needles and on into the charcoal cannister. Someone
on the list had that problem within the last week. In your case, it was
demonstrated when the tank vented on you. In one episode on my GT, gas
spewed both out the back and out the cannister.
So, the answer is to clear the obstruction in the vent line. Looking
at the lines, you will find that one runs back toward the fuel tank, and
another runs to the carbs. You need to clear the line that runs back.
Disconnect the line at the tank in the fender. With an air hose or a
healthy set of lungs, blow on that line. When it clears, a brown, sludgy
mess will spatter out, a secret blend of gas, rust, water, cobwebs and
more. Once that line is clear, disconnect the lines from the can in the
fender and clear it also. Then, you can remove the gas cap try blowing
back from the fender can line into the tank. Listen for bubbles.
Somewhere in the WS manual it says to replace the charcoal from time to
time, and if it gets wet with gasoline. Some say that is not necessary.
Whatever, few change it. If you open up the cannister, you will see a
Mercedes-Benz star-shaped retainer with a foam pad. This may come flying
up at your face, since there is a robust spring underneath, so keep your
hand over it while disassembling, and do the work in a dishpan. By the
time I got mine apart, the charcoal was all dry. I re used it, though you
can get charcoal at the fishtank filter section of a pet store. The
foam filter under/over the charcoal will probably come apart in your
fingers. I cut up Scotchbrite pad to size, figuring that it was gas
resistant and would permit air to flow through it in both directions. By
the way, the Novus polish for rear windows will put a splendid shine on
the charcoal cannister.
Once I figured this out and sorted it out, the engine ran better than
it had before the incident of spewing fuel. Perhaps it was partly plugged
and causing the engine to run rich from extra pressure. I don't know what
the exact cause was, but the odd periods of running rich and stalling at
stoplights ended and fuel mileage improved, so I suspect that this vent
line was partly plugged for a long time.
I hope the cleanout goes as easily for you as it did for me, and that
the result is as satisfactory.
Bob
'72 GT
On Mon, 20 Sep 1999 08:09:28 -0700 "Walt Goddard" <waltcpa@sierra.net>
writes:
>Hello all,
>
>Went to put gas in the 77B on Friday and there was a tremendous (at
>least
>it seemed that way to me) amount of pressurized air in the fuel tank.
>Had
>to remove the cap VERY slowly and still had a lot of air pushing it
>out. Is
>that a normal condition? I bought an aftermarket locking gas cap from
>my
>local Car Quest when the old one broke, but didn't pay attention to
>whether
>it should be vented or not. TIA.
>On the positive side, seems unlikely there are any leaks!!
>
>Walt Goddard
>waltcpa@sierra.net
>
>
>
|