My 625 SXC had the Mikuni BST 40 carb on it. Bike ran fine. Since I am in the bike parting out business, I got a FCR 41mm carb from a 2005 525SMC and replaced the Mikuni. I know the Euro spec bikes have this carb. I did nothing but adjust the throttle on it. What a huge difference. First off the bike starts up really easy now, be for it was a pain. The bike response so much better too. Getting the airbox on the carb was not easy but I got it on and it ain't comming loose. I would recommend the Keihin FCR over the Mikuni. A little pricy, but a much better deal. I got my 625SXC rather cheap. The starter clutch (free-wheel foward) was chewed up. and the bike was hard on batteries. I hear starting on this modal was an issue. Now with this carb, it starts as easy as my Honda 230L did and I almost never have to choke. The FCR carb also has no throttle sensor like the Mikuni, the only thing I sensed with the BST carb was that it didn't work well, I have come to the conclusion the Mikuni BST carb is garbage. I never even checked the jets, no clue what they even are (probably the 525SMR jetting). I live more or less at sea level. Just rode up in the Sequoias up to around 8,000 feet no issues at all.