I hqve a 1999 sporster and I bored it from 883 to a 1200 I also upgraded to vancin pipes and upgraded a air filter . It start up and sounds pretty good I may need to reset a size or so bigger . my problem and question is the rear pipe within minutes began to get hat and discoloration ...There from the still looks excellent but rear looks bad any idea why? And any idea how to fix it?

 

Shawn, welcome to HDF from the UK. I suggest your starting point should be set up your carb to 1200 settings as a starting point for making further fine adjustments.