i looked into this for a bit B4 i decided that NSR 250s were the best 250 for the street. Really your only non total loss system is to put in a TZR motor and charging assembly. maybe good for 70 hp at best with some good tuners..?

do you really wanna ride a TZ on the street? race gas, rebuilds every few rides... hmm those clutches are terrible for take offs at a race... i cant imagine stop and go traffic with one.. probably need new plates after every few rides too... super peaky power with no torque or mid power..

sounds good initially but once you look into it, its really not such a good plan. http://www.tz250racing.com/ is a good place to get more info
there is a guy who made a total loss tz 250 for the street there...
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Koren
2 Strokes and I'm Off