[Mgs] MGB driving me nuts

[Bob Howard]

Paul,
   The vent line was plugged, which was confirmed when the compressed air
hose blew a rusty, viscous sludge out of the line into a cup.  
    This is a car I bought well used, so I do not know if the tank were
the original or a correct tank. It had been off the car at some time, as
the rubber packing strips that should have been present were not present
when I removed the tank.  
    It could be that there were two issues: the blocked fuel vent line,
as the carbon cannister did overflow and the tank had pressure,  and
there was flooding of the HIF carbs.  
    Our home is in a valley that chills well below area temperatures at
night.  I filled the tank that morning at a near-by fuel station, then
driven only a mile or two before parking it in a large asphalt lot on the
clear, sunny day, during which the air temp rose some 30 degrees.  Mid
afternoon I returned to the MG, smelled the fuel, tried to start it,
found gasoline dripping onto the ground and onto passenger side (USA)
carpet, pressure in the tank, etc.
    One by one, little problems of this sort get resolved. 
Bob
 

On Fri, 5 Sep 2008 09:18:30 +0100 "Paul Hunt"
<paul.hunt1 at blueyonder.co.uk> writes:
Several oddities here.  If the fuel in the tank was expanding, causing a
'whoosh' when you removed the filler cap and spurting out of the filler
hole, then the vent was blocked which would mean that fuel from the tank
couldn't flood the carbs.  The tank should have a limiting chamber that
is designed to prevent fuel leaking from the filler on expansion, unless
its bleed vent were blocked or a non-limited tank was installed.  If the
vent were not blocked, then expansion would run into the canister and
from there onto the ground.  It couldn't get to the carbs unless there
were other blockages in the canister plumbing.  If the outlet to the
canister were blocked, but the tank vent were not, then there is a
possibility of *air* pressure from the tank going into carb vents, which
would push the fuel level down in the float bowl and consequently up out
of the jet, so flooding the engine, possibly emptying the float bowls. 
The carbs may flood themselves if the float level is too high, simply
from expansion of the fuel in the float chamber and nothing else.  But
that has never happened on my V8, when switching off on very hot days I
can hear the fuel boiling in the float bowls and see fumes pouring out of
the vent, but no fuel dripping out and no flooding.  When I do restart
some time after that the fuel pump chatters away like mad for several
seconds as it is having to refill both float bowls.

PaulH.   
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