Workshop Manuals
I've recently found the Official Workshop Manuals for the "1988 DT125R" and "2005 DT125RE, DT125X".
The 1988 model had a different carburettor (round top), to the other models up to 2003. This manual covers the YPVS power-valve and servo, and setting up. The YPVS servo in this manual is the 3-wire type.
The Manuals are in PDF Format and you'll need Adobe PDF Reader to view them.
To Download the manuals, "Right-click" the images and select "Save Target as...":