Well I did it...... no, not the install, but the purchase. I got a 39mm FCR-MX off a Yamaha 450. It has the air-cut valve to enrichen the pilot circuit automatically on decel. Bye bye popping! I've done a lot of studying and feel the 39mm FCR-MX is the perfect carb for the DR650. The FCR's ingenious bearinged slide and floating slide seal is superior to a standard slide carb. Low end response and mixture accuracy is greatly improved with this set-up. That's what I'm most looking forward to is the low end response and torque improvement with this carb. I'm sure there will be gains everywhere but I wanted to focus on the area that the DR makes it's best power. I'm not a big beleiver in the "four-barrel on a moped syndrom" I sent many emails talking with Sudco (imagine that) about clearances and measurements as the MX version is a bigger carb than the standard FCR. I'm certain I can get it to fit. A new 39mm FCR-MX from Sudco with the air-cut valve is $530. I got the carb for $200 off eBay. I figure the most I'll have to spend on jetting is around $75 worse case senario. I'm figuring it will be less. I will have to make an aluminum air boot adapter for the back of the FCR to reach the DR's boot. No biggie... I've made many a machined adapter to graft carbs before. My bike isn't here from San Diego yet and the carb I just bought a few minutes ago so it will take a bit of time before I start playing around with the install. I'll post a full pictured install and the jetting process. Stay tuned!