Hi mate
I went through the same deal with my wr400 and was told i might be able to fit bits of a wr450
onto the carb but the cheapest and better option is a Dr D hot start complete assembly.
look on the Dr D web site.http://www.dubachracing.com/cart/index.php?main_page=product_info&cPath=4&products_id=34 Its one of the best things i put on the bike.
cheers
