Hmmm...now that i've been riding it a bit, the slow-rundown seems to have resolved itself.  However, sewing machine-like valve noise is same as ever (interesting how variable it is, only partially related to temperaturs).

Anyway, I've noticed a bit more backfiring.  Not sure if it's because I'm being a bit less cautious in shifting (because I'm getting more comfortable riding), or if it's my new and maybe-improved(??) valve clearances.

Should I jump into tuning the carb?  It looks like the previous owner may have already taken out the brass plug for me.  Can the adjusted valve clearances affect the backfiring amount?  (It seems that it would, but I'm a software guy, not a hardware guy )

Have ya tried shifting w/o the clutch yet?

Mine backfires/afterfires only when closing the throttle and coasting and the engine rpm's drops down to about a little over 3,000. Not above and not below that.

An update...

Inspired by Chris Roth's post on a similar issue, I decided to check *my* decompression shaft.  So I figured I'd give it a shot.  Since the manual says that it might be possible to remove the cylinder head cover without unmounting the engine, I thought I'd try.

I succeeded!  It was not easy, but only 10minutes of gymnastics got it off.

Upon initial inspection I didn't see anything obvious, but then looking on the bottom of the rocker arm, where it rides on the camshaft, I noticed that it was CONCAVE rather than convex, like the intake valve.  And there was a thin, sharp sliver on the edge of this, which likely (to my software engineer eyes) means that the camshaft was grinding that sucker down while the previous owner was running without oil.  And that the new free space give the rocker arm a lot of room to buck about in a way that was not intended.

(When I bought the bike, my uncle took one look at the bluing on the pipe and said "I think that bike's been run without oil.")

So I've ordered a new rocker arm (and some red Permatex).  The camshaft doesn't seem to be obviously bad (It's still in the engine with the chain on it, so it's just been visual/feel to evaluate it).  The rocker arm pad is ground down about .75mm.

So I'm hoping for some advice....Can I get away with just replacing the arm (and checking the other stuff in the head cover), or should I really look for more trouble by taking off the engine?  Taking the head cover off wasn't so bad, but I wonder how easy it will be to get the cover back on without botching the sealant.  

I know to the veterans around here, it's a no brainer, because they probably have engines sitting on their coffee tables   But I don't want to get overrun with parts everywhere in my garage, and I don't want to get in over my head.

Thanks for your support!

Took the bike out now that it's back in action, and it runs great.  Sounds great (if you like quiet...maybe I'll look into the dyno )  Seems to have a shade more power as well.  

Thanks to this forum, I fixed the dang thing.  I'd never have had the confidence or the knowhow to work on this bike if it weren't for suzukisavage.com, for sure.