yes rejetting is a must with the jardine. Look in the Marketplace section  in the post JETSETS.  Lancer will sell ya ya need for the rejet and white spacer mod.  I also have a Jardine. Im running the 152.5 main jet and the 52.5 pilot jet with 1 washer on the needle jet. running really strong now with hardly any backfire.  I also modded my jardine muffler. I removed the baffle and on the inlet side of the baffle I tack welded a peice of steel mesh probably 1/2" by 1/2" squares. Then put the baffle back in. Next I got 3 of them stainless steel brillo ,scrub , thingys and stuffed them into the inlet of the muffler.  the steel mesh keeps the scrub pads from shooting out.  The sound is a awsome rumble now.  Still loud , but not annoying loud.  Also helped out gaining more back pressure, now i got the carb tuned properly.

Just FYI,I put on a Jardine on my 2k Savvy.  I didn't rejet or make any other mods.  Sure it pops and snaps on occasion, but nothing too bad.  After about 1500 miles the header still isn't bluing either.  It's just sort of a uniform tan color.  Again, nothing I'm concerned about.  Also I do tend to ride conservatively.  It sure does sound better though, just keep the throttle use to a minimum...