Apparently rain had entered the exhaust system through the exhaust pipe outlet hole,
you know that funny little tube at the end of the muffler, and because the engine was
mounted above the wing the muffler had filled with water, and then the water had entered
the engine via the exhaust port.
A cheap remedy for the problem is to cover the engine, I read somewhere that a plastic
garbage bag would do the trick but I found that a garbage bag causes condensation to form
when the sun beats down on it. Another suggested solution was a canvas cover but I found
it wasn't waterproof. A solution that works very well and is quite inexpensive is a
backyard BAR-B-QUE COVER.
They are generally available at most hardware stores, or Canadian Tire Stores in Canada
are waterproof, cheap, and come with a tightening string or cord around the bottom, are
available in different sizes and come with a heat protection shield inside, so you don't
have to wait around half an hour, for your engine to cool down before you put the cover
With a little alteration, simply closing the opening a little at the top they also make
an ideal cover for your parachute, keeping it dry, and protected from harmful sunlight,
and Mother Nature.