I have a gasoline engine 87 Syncro.  When I fill it up, the automatic
cutoff valve on the gas pump shuts off the flow but I only have between 1/2
to 3/4's of a tank indicated on my fuel gauge.  This happens on every gas
pump I've tried.  If I force feed the additional gas into the tank, by a
manual very slow process, sometimes rocking the van, I can get the fuel
gauge up to the full mark.  Anyone have any idea what is going on and the
necessary steps which will rectify the situation?  Is there a vent that is
possibly blocked to release the back pressure?
Thanks,
Jon