The gas gauge on my '79 Westy has suddenly taken on strange behaviour.  It
reads full upon fill-up, but right around the half-way mark, it soon reads
way below empty (like right on the pin)  I haven't actually observed it
drop, being too busy driving, but refilling has proven that it happens when
the tank is roughly half-empty (half-full, if you're an optimist!)

What's the explanation for this, and how easy is it to fix?  I'm having the
engine out for a major overhaul soon, so maybe that's the time for this
problem, too?

Thanks, all.

Roger