I started running a cr250 and absolutely love it, so much power and even on a small track, it will pull off the corner just as well as the 4 strokes. Mine is a stock 03' unit, running 520 chain setup w radiator. The kart scales out well and overall weight is right inline with UAS, so not interested in removing anything to lessen it. If. Can manage to hang on to it for a full night of racing I'm sure it'll be up front, my last race out , I have some of the fastest lap times in the field. From what I can tell, it will be much less maintenance than most traditional open motors, just pricy to get it all bolted up for the 1st time, but if you can fabricate parts, you won't be disappointed in the end result.
Matt