Here's the Yamaha WR250R service manual on video, click to pause it one the section your need.
Or email Dave, he can send you a copy as a PDF, or will send you a password to look at the manual scan on his web page
if your after the crf 250 l it share the same engine as the road base cbr 250 single road bike. Nice engine but not in a dirt bike . Only because of gear box ratio s.