Hi All,
I have just bought my first bike, a used 2007 S40 with 2800 mi. Loving it except for the backfiring. I enjoy the odd one here & there, but I live in a hilly area and when engine braking on steep ones it gets annoying. I would like to adjust the fuel/air mixture, but I need some detailed instruction. Brass plug on the RH side? Drill it out? Which direction to turn screw? etc.
Thanks,
Mike

also check the torque on the header bolts, 15 to 20 ft-lbs on a cold morning, no start till checked.

also check the muffler clamp, anytime, but I suggest cool to the touche.  

Where are you?

I'm in Hollywood CA

good links to the tech reference site, but the step by step for the brass plug removal could use some pictures.  seems different people have different techniques.  also seems people drill too deeply and mess up the screw under the cap.  pics of a successful removal would be really helpful.  thanks!

Ok Calikid ...here's what you do for that backfire. You are going to need a drill and drill bit, large screw, large screwdriver, pliers and small screwdriver. here's what you do ... Drill the middle of the brass plug on the right side of the carbureator ... do not just send the drill bit thru because you do not want to damage the gas adjustment screw behind the brass plug. You want the hole just big enough for the large screw ... with the screw and large screwdriver turn it into the hole you have drilled ... you want to just get the screw stuck in the brass plug but not go all the way thru to damage behind it. Get your pliers, grab hold of the screwhead, leaverage yourself and pull the brass plug out. Take your small screw driver and turn the adjustment screw a half a turn counterclockwise ... stop. That's it.
I have the 2007 stock bike ... pipes and carbureator and did this adjustment ... the engine and muffler runs and sounds so much better.

Good luck.

The brass plug is meant to keep you from adjusting the lean setting ... when you hear and see the difference from the minor adjustment  I explained YOU WILL LIKE IT ... the engine and muffler sounds like it is supposed to be. My judgement  ... and take it for what it is worth ... you want your bike to run like this and not on the lean setting. If you feel uncomfortable with the adjustment ... just turn the screw clockwise a half a turn and you are back where you started. I have not gauged the gas factor after the adjustment yet ... I can tell you I will not set it back to run like it was on the lean setting. I am not a technical guru like the others here when the talk about in the long run your bike running lean makes it run hot ... and will wear out parts sooner. The bike runs better with the minor adjustment ... the tech at the dealership shop told me this is what he does when customers complain about the backfiring. I did it ... I love it ... I put the information here if anyone wants to try it.

TheCaliKid wrote on 09/16/08 at 18:56:59:



It's documented on my blog with pictures that should answer all your questions.  It is really an easy mod to do.

Here's the link:

http://essforty.blogspot.com/2008/09/idle-mixture-screw-adjustment.html

That's exactly how I did it. Here's the pics of drilling, then the drywall screw in the brass plug, then the screw adjustment.





And then this shows the exposed idle mixture screw being adjusted.



I documented it in more detail on my blog since I had to post the pics there anyway.  I've also posted it in the tech docs section as well since I did not see any pictures in the existing thread.  

http://essforty.blogspot.com/2008/09/idle-mixture-screw-adjustment.html