I have 500 miles on my 2007 S40 and the pipe is turning blue starting at the motor for about 10 inches down the pipe. I'm thinking the mixture is a bit lean.
This weekend I pulled out the brass plug and adjusted the idle jet and that made it idle better and pop less. Then I took of the seat and peaked under the fuel tank. The frame is in the way of removing the top of the carburetor. How is everyone getting into the works of the carb? Are you removing the carb completely?
I ordered the shop manual but it's on back order so I'm guessing a bit on where things are. It looks like the top of the carburetor has a diaphram under it that lifts the slide as vacuum increases and I'm guessing that the needle(s) hang from that slide. I'm further guessing there is a white spacer that is easy to see with a tag on it saying "remove this spacer for top performance"

Well, maybe not, but I'm hoping that it is obvious. I'm not sure what a pilot jet is vs. a main jet unless it is some kind of mid range jet.
I'm wondering if my guesses are close enough to get me though this or if I should wait for the manual to arrive and hope my exaust pipe doesn't get too ugly in the meantime.
It would be nice to see a picture of a semi-exploded BS40 showing the spacer and other innards.