Both the MS261 and MS261CM are available. The 261 has a carb which adjusts just like the carb on your 250. The 261CM has an electronically-adjusted carb (so-called Mtronic carb)...no adjustments needed or possible.Lastly my concern is serviceability. Despite the one issue I've been battling on this 250, I knew the saw in and out. Like the easy carb adjustment screws on the side and ability to change my own spark plug, filter, sprockets, clutch, etc... is the 261 as serviceable? I don't think the carb adjustments are on the outside of the saw - is that an issue for a guy like me?
Both systems are well proven and are dependable. Your choice.
As others mentioned, sell the 250 with the bars/chains and buy the new saw with a 18" bar.
You'll love it.
Roy