On the powervalve subject. I lived in Spain for 6 months and actually saw a yami DT200 in person. Quick review: it is the blaster motor liquid cooled with powervalves. Stock blaster: 17 hp Stock dt200: 31hp it is a bolt on conversion. I never did find one, but I bet a valved shee would really gain some grunt.
I never did find a dt top end in my 6 months of searching every scrap yard in castilla-leon...