I have read many posts here about removing the plastic spacer washer in the carberator to give a richer mixture. I have a 2004 Savage, with 1200km, just completed the initial service. My bike does not backfire, except for a small fart when shutting it down. It also seems to run fine at all power bands. I have noted a slight yellow discoloration to the header pipe immediately at the engine join.

Should I remove that spacer as suggested by many if I am not seeing problems (ie "if it ain't broke don't fix it??")?? Is that yellow discolouration the sign of bluing to come?

Any comments and suggestions appreciated.

You're pipes are going to discolor. Coloring depends on mixture and heat emitted. Gold and/or blue. There are lots of threads on the spacer issue to richen the mixture up and decrease backfiring. Removing the spacer (or replacing it with the radio shack #4) isn't going to change your pipes discoloring. The big single discolors regardless of what you do. That's just the way it is. You can find threads for what products others use who don't like the discoloration to clean it up. Some like it, some don't. If your bike only gives a little puff when you shut it off, I wouldn't change it myself... Have you done any hard decelerations and had backfires? If so, then you may want to if you don't like the noise but its not hurting your bike any.

They run from the factory that way so change it if you like, or leave it alone... its a matter of personal taste.

I think that the stock header on any Savage is going to turn golden at the exhaust end.  Just the nature of the beast, and re-jetting won't change that.  I believe that it will stay the same as long as the bike is operated normally and not allowed to overheat.