Hey, new guy here.  I just bought a '05 S40 for the wife.  Pretty cool little bike, but there is a LOUD backfire whenever the bike is run for a while and shut off.  In looking through the posts here, this seems to be a chronic condition for these engines.  To me this suggests a lean condition.  If this in fact is the case, would choking the bike prior to shutting it off minimize the backfire, and will doing so potentially cause any damage (due to back pressure)?  I do realize that carb adjustments may improve this condition, but other than the backfire it runs great.  My preference is to keep it stock.    

Thanks in advance for your comments.    Ray

Hey Raynman, Mine does the same thing. I have a jardine slipon exhaust, 1/2 spacer mod, rejetted to 55 pilot and 152.5 main. I have gotten rid of most of the backfiring, but still get a loud BANG at shutdown. My solution to this is to keep it in 1st gear at shutdown and gently let out the clutch until it dies, rather than using the kill switch. That is the only way I've gotten it to not BANG at shutdown. I don't mind the bang so much when shutting down at home, but at bike nights or places like that, it's definitely a little embarrassing to say the least  

Mine is a stock 96.

I adjusted the pilot idle screw per sweet spot in the rpm at idle method and pow! at shut off.

Then I gave a quarter turn (back to the way I got it) and puff on shut off.

Of course later it developed a pow! with every decel (great way to get rid of tail gaters) that turned out to be a header leak.  If I could get that on command.  

verslagen1 wrote on 12/31/69 at 16:00:05:



Before I bypassed the sidestand switch I used that at stoplights when someone had their obnoxious stereo so loud it bugged me, just put it in 1st, wind it up, use a heel on the sidestand & Bang,, makes me jump, now I have to use the kill switch, & that's not always such a stealthy maneuver.

justin_o_guy wrote on 12/31/69 at 16:00:05:


How anti something or other of you - aren't you ashame

Five_Points wrote on 12/31/69 at 16:00:05:


Mine backfires every time I shut it off and I get a little blue flame shoot out the exhaust. I count to 3 and then point at the exhaust on 4, it backfires, and people think it's really cool at bike nights.

So don't be embarassed - it's part of the bike's character, and i love it!

Update - Choking the engine just prior to shutting down really does minimize (if not eliminate) the problem.  Makes sense, as the backfire is caused by a lean condition.  Anyway, my wife is much happier now that she doesn't have to take cover when shutting down.