I've worked on them, never gave a thought about a manual?
If you go to the Valley View website and look at the VV-40, there is a link to a nice detailed review of the engine.
If you go to Tower Hobbies and the DLE 40 twin, you can down load their manual for the DLE 40 which is much like the VV- 40. But the manual is like the previous Tower produced manuals, it has some inaccuracies such as proclaiming that you set the ignition at 44 degrees before top dead center. I get the idea some young lady wrote the manual.