The XT's had a "cold start valve" (equivalent to a choke) that automatically adjusted the fuel mixture to compensate for cold start-up. I'm sure the SVX has something akin to this, and that yours is not functioning (probably not at all). Mine starts and immediately idles at 1,500 to 1,700, then gradually lowers. I'm sure someone else on this board can figure your trouble out a lot more precisely...