I have an '05 DRZ-SM with Yosh Pipe and a 39mm FCR Flat Carb.
It also has the air box opened up and a KN filter. I installed the jetting that Burned says works, but had a problem with popping with closed throttle at high RPMs. I also had problem with slight bog when going from idle to wide open throttle. For the bog I made an extra spring that fits inside the stock spring on this style FCR. I know the trick for the MX FCR is to safety wire the linkage, so you get a harder shot. The extra spring does the same thing for the flat FCR. With the carb off the bike, it will shoot fuel about 10 ft.. Then I talked to a friend at Mad Brothers Racing, in Easton, PA. We looked at the plug and determined I was lean on the top. I changed to a 165 main, and that made a big change in the way the bike pulls. It will power the wheel up in second gear with just little pull on the bars. It would not do that before. Still working on the popping. If I put in a 48 pilot and open the screw 3 turns it does not pop at all, but the screw will not stay in. I just put the 45 pilot back in, and am going try to work on it later today.