To set the valves, you need two feeler gauges: 1-0.040mm and 1-.10mm. When you adjust the valves, you turn the engine so that it is at Top Dead Center with both valves closed. If the valves tend to be open a bit, you need to turn the crankshaft 360 degrees. Then you set the valves so that the thin feeler fits and the thick one doesn't.

Setting procedure also comes with the O.S. tool set:

OSMG6334 72200060 GAUGES TOOLS 4-STROKE US$11.99

These parts can be ordered through any hobby retailer who sells O.S. Max engines and accessories.