I have a 2007 S40 and have been having problems with my bike popping on decel and when I shut it off.  I've checked the Petcock for leaks and it seems to be ok, I've adjusted the idle speed and have all but eliminated the popping on decel, but now I get a huge pop a few seconds after I shut down the bike.  (and blue flame out of the exhaust)  Last week when I started having the problem I realized that one of the bolts on the header pipe was loose.  I've since tightened this down, but wonder if there is a problem with the gasket?  Any ideas for what I should try next?  Thanks for your help!

Thanks Dave.. I read through these threads and think that it may need the idle mixture adjusted.  The last thread seems to be the best resource for this, but one person seemed to think it was because it was rich, while another said it was just a hair thin.  I guess I could remove the cover to this screw and give it a few small adjustments to see if it helps.