Well, I drilled three 1/4" holes in the stock muffler baffle last night, and pulled all the fiberglass out of the cute little sound absorber in there (See "This muffler is screwed" thread.)  Then, today I spent way too much time washing, waxing, and polishing metal.  I decided to take it for a little run and then fiddle with the carb in case the muffler change had messed things up.

I ran it down the highway to get it good and warm, pulled in the yard, and spent 4 or 5 minutes tinkering and listening.  Finally settled on about 2 turns on the pilot screw, although I don't hear all that great a difference in the idle no matter where it is set.

Then I shut the bike off, and heard a strange boiling sound in or very near the carb.  It sounded a lot like water poured on a hot stove, only muffled from being inside of something.  This went on for a minute or more and finally fizzled out.

I checked the oil both before and after the ride, and it looks good.  It's fairly new synthetic.  Outdoor temp is cool, and my ride was not especially hard, so I can't see the bike being too hot.  

Anyone have an idea what this sound could be, and what may be causing it?  It's the first time I've heard it, but that doesn't mean it is the first time it's happened.  I had my head right down there next to the engine when I heard it.

Edit:  Maybe another good way to describe the sound would be "frozen potatoes hitting hot grease in a covered fry pan."

Well, it was 3-4 hours after I washed it, but I suppose there could have been some water pooled in there somewhere.  I hadn't thought of that!  That would be a huge relief.

Maybe the spark plug hole?  That would hold water for a long time I suppose.  

I'm feeling better and better.  I thought maybe fooling with the muffler had fried my muffler bearing, or knocked loose the defibrillator cap, or something.  That is often the result of my misguided tinkering.

But it's just so fun to fool around with this bike.  Sometimes I feel like the puppy who looks around at the destruction he has commited while his master is away and wonders "Now who did that?"