Did you happen to mean VM34's from TC Bros? That would make more sense as I don't think they sell BS34's carbs...and if considering it, just note that they will also need to be tuned regardless of what they say has been done to make them XS650 appropriate. But VM's are super simple and tuning them is a breeze. You'll need new intakes. You'll also need a two-into-one throttle cable. Get a few pilot and main jets in various sizes, as no two bikes will be the same with jetting. (There are a few threads on here that provide good info on tuning these and jetting combinations that seem to work well). I personally have VM34's and I like them. I don't know if they are better than really well tuned BS38's, though to be honest. But they are easy and I like the way they look/perform.