I have a 2007 S40 which backfires. I've obtained some replacement pilot jets and read, here, the strategies for eliminating backfire. The first, adjusting the idle mix screw, was attempted by the previous owner, who stripped the idle mix screw head. I'm considering buying a used carb on eBay and tinkering with that instead of this already somewhat bunged-up carb. I haven't been able to find a 2007 but did find a 2000. Has the carb changed in the period from 2000 to 2007, or will I be able to modify the older carb, clean it up, and use it? If the answer is, "it's different," what model years will substitute for the 2007, assuming I can't find a 2007?

Also: Any tips on removing the stuck idle mix screw also appreciated, as plan B is to remove and replace it. I'm considering using a small chisel and tapping lightly to see if I can get some purchase on the stripped slot, or drilling a small hole in the screw and using an easy out, but these both seem to have the potential of damaging the threads.

Thanks,
David

I think this is an epidemic, and I think it is contagious please isolate your Carb until it is better.  I think others should make sure and vaccinate against this bug before it causes too many casualties.  

Seriously…..  
I had the same issue; the previous owner totally stripped the head of my screw.  I tried to "easy out mine" and totally messed it up.  Someone suggested a machine shop for getting our broken bolts on another issue.  I wonder if a machine shop could do it for you.  I WOULD NOT RECOMEND DOING IT YOURSELF.  

E-bay has them for sale used sometimes, and from what I understand any year will work fine.  

Because of the cost of the thing, I would not recommend going at it half a$$ed.

Craftsman screwdrivers have a serated face for gripping the screw better.  I might take one of these and modify it, grind the tip to sharpen it, half the tip going one way, half the other.  So you could take a hammer and tap it into the screw to bite.  Then apply a lot of force into the screw to keep it engaged while applying torque.  A little pen oil and a lot of prayer.  

If I'm able to get the idle mix screw out, I'm assuming I can probably file a new screwdriver slot and replace it. Does it have any kind of attached spring I have to be careful not to lose? And if I can't get a functional slot in it, what part number should I be looking for to replace it? The blow-up diagrams I've seen of similar carbs on motorcycle parts sites are so poor it's hard to tell what the idle mix screw is, and they identify all screws as "screw."

Thanks again. Screw is soaking in PB Blaster and will tackle it tomorrow, if it stops raining.