If you're not fussed about getting a 400, you'll make life a lot easier by forgetting two strokes!
The are technically illegal in the US, and if you do a search for 'titling' on here, you'll read all the painful stories from those who've done it. It can be done, but if you are not bothered whether you get a 2 or a 4 stroke, buy a 4, it'll be easier to sell on after too.
Now, having shot myself in the foot as a two stroke enthusiast, I can heartily recommend any 250 2 stroke! They are out there, and you can get them in to the country, just don't expect it to be easy if you live in a tight ass state!
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