I'll agree with Dan.  I spent much time trying to get the '80 Westy
running again -- it was flooding the engine, typically during startup
only.  I *believe* the final problem was odd contact at the distributor
Hall effect generator.  Getting this part wet could do the same thing.
My belief is that the engine was reverting to open-loop mode on the
fuel injection, and that it was getting spurious signals from the
coil, acting like it was getting many sparks.  Consequently, it got
many extra squirts of fuel and flooded the engine.  My way home was to
pull a major pipe off the intake manifold creating a massive leak and
restart the car (the *very* lean condition allowing the flooded engine
to fire).  Then reconnect, and hopefully make it down the road some more.

I ended up removing the wires from the plug housing and soldering the ends.
I then sealed the plug with RTV.  I screwed up and wired it all back together
backwards, too, but that is another story.

In any event, water in this plug (and it conveniently holds water -- the
socket does not drain) can cause extra "sparks" to happen, which the
computer translates to pulses of fuel.  If the O2 sensor is momentarily
lost, the ECU will revert to open-loop mode, and this extra fuel will be
disasterous.  Restarting the car will clear the ECU and it will go back
to closed-loop mode while it can -- and the extra pulses will not be
a problem.  Full-throttle and idle (on a Digifant, but not on my '80)
will cause the ECU to enter open-loop mode again, which could explain why
you kept getting this effect.  There is supposed to be a water-tight boot
on this plug -- mine is all cracked.

It might explain your troubles -- the distributor getting wet could have
done this.  Next time, seal the whole shebang in a plastic bag before
driving in the wet.  Also seal the Idle Stabilizer Control box in a plastic
bag -- the protection it gets is minimal (I also seal the case with RTV).
I'd do the same for the AFC connector as well.

I think a good O2 sensor, with a sealed wire, should not notice a dunking.
I have done the cheapo-splice routine, though, and had to get the splice quite
watertight.  The spade-lug connector is supposed to be in a watertight
fitting, but mine is all cracked.  On the '80, the temp sensor connector is
*not* a watertight one, and when this gets wet, it can cause open loop mode
as well.  I don't recall how they are connected on later engines, but sealing
this connection also would make sense.

I don't know if you can seal the coil -- putting it in a plastic bag might
not be good as they generate a lot of heat.  you might be able to seal just
the wire end, and leave the can part exposed for cooling.

Good luck.  I hope and trust that the problem went away when it was all dried
out.

Malcolm