Alright, so I run with a Jardine exhaust on a 2009 S40 and LOVE the way it sounds. However, I have had a HELL of a time getting it to run without constant backfires and shut-off poofs. Reading through the site I picked up the vibe that a lot of folks running this exhaust have a hard time with it. I think I've finally got mine about right, though- with some VERY much appreciated help from LANCER and several other members here- and figured I'd share the info in case someone else could use it. If this is repetitive or pointless, feel free to ignore (dear reader) or delete (moderators).

 

The bike: a 2009 S40 with 4200 miles. Raptor Petcock installed.

Location San Antonio, TX about 1000 feet above sea level. The temps over the latest tuning adjustments have ranged from low 50s to low 80s (I know...Texas in the "winter").  

Filter: Uni foam filter

Exhaust: The Jardine is welded on. I highly recomend this, because I could not get mine to seal any other way and it is impossible to eliminate backfire with an exhaust leak.

Jetting:  55 pilot jet, one spacer on the jet needle and a 152.5 main jet.

Air Mix: currently turned out 2.5 turns.    

Results: Right now I have only the slightest backfire when I TRY to make it backfire. Power at low and mid-range is significantly improved. I weigh in at 185 lbs. and have no problem pushing it above 90 on relatively level highway, so I don't feel any shortage in high end, either.
  I feel like I may be running a little rich at 2.5 turns out (this is a nose test, just sniffing exhaust fumes), but since I'm lazy I am not going to pull the plug to check. My plan is to just creep the mix screw back an 1/8 turn at a time during my next long ride and nail down EXACTLY where the mix starts to run lean.
  If I run with the choke 1/2 out it feels like I lose some low-end response, but the exhaust burbles and gargles and snaps and sounds awesome. I'd love for it to do that all the time, but I'm not going to richen the mix that much to do it. Right now it is a steady, even growl throughout.

Things I tried before: It ran too rich with a 155 main jet. It ran too lean with a stock pilot jet. 3/4 spacer improved the backfiring, but not as much as I wanted. 1/2 spacer improved backfiring more, but I GAINED a shut-off poof. Not cool. 1/4 spacer eliminated shut-off poof and furhter improved backfires. I may be over doing it and per Lancer's advice I'll probably jump back up to 1/2 and see how it does at the current tuning. My air-mix was all over the place during this process, probably becuase I was doing it wrong.

My two cents:  Take your time and make sure the bike is warm before adjusting the mix. Try and tune at the same relative weather conditions if you can. Weld your pipe if you have ANY doubt there is an air leak. Tape up your throttle housing and mark off throttle position so you can nail down what circuit is causing the issues. I spent a lot of time thinking my mix at the needle was causing my problems, only to find out the majority of my backfires were happening below 1/4 throttle. It was much easier to sort out this way. Also, when removing the tank and pulling on cables and stuff to get carbs and air filters in and out, ALWAYS RECHECK YOUR CLUTCH CABLE TENSION. Sometimes it can get pulle out of whack and might cuase some drama when out on a ride with your friends. I've been told, anyway. Happened to this guy I know...

  That was long. Hope it helps someone out.