It's pretty easy but since this is the pump section not the engine section.....
4 to 6 thousandths each valve or 0.1 to 0.15 mm
Adjust only if you are having performance problems and suspect it is the valves.
To adjust valve lash, remove cover that has OHV stamped on it, this will get you to the adjustment end of the valves. You will see two rockers, IPB page 3, #1029, and two set screws with nuts on them, IPB page 3, #192. These are the adjusters. Rotate engine so that one of the valves is being used, as in the rocker pushes on the valve stem and pushes it down toward the engine. The other valve is now fully retracted in to it's seat and is ready to be adjusted. Using proper tools, loosen the nut on the set screw while holding the set screw with proper tool, probably a metric allen wrench. Keep the set screw from moving while loosening the nut. Now take your feeler gauge and slip it between the valve stem and the rocker arm. Adjust the set screw so that the feeler gauge has a slight drag on it when you slide it back and forth. Tighten the nut while holding the set screw from moving. Check your work, if it has tightened or loosened the drag, you will have to do it again this time allowing a little leeway so that when you tighten the nut again it doesn't cause the lash setting to be wrong. Takes a little practice but nearly anyone who can use a wrench in each hand at the same time can do it.
Now do the same for the other valve. Once you are satisfied, put the cover back on. You can test run the engine with the cover off, will only be a little oil splashing out, just a few drops.
This is still the pump section, but never said I didn't know a little about small engines!!