Yup, Japan is in Asia. However, I wasn't sure what all of Asia used so I just went with what I knew to be true.
RON 91 is PON (USA/Canada) 87. USA uses PON (R+M/2, technically). Ah, the little things that they don't tell you, right? This is one of those things you have to find out yourself or be taught in a school about building/maintaining/tuning engines. This is why everyone thinks the EU has higher octane, and therefor better quality fuel, than the US does. In fact, it's the same stuff just using a different numbering system. Their 98 RON is our 92/93 PON we get out of a pump. Think of it like us using Imperial and the rest of the world using Metric!
CRC is pretty high powered stuff. I have good experience with SeaFoam and know it won't damage your motor or fuel pump, even if you use the whole can at once. The other thing is, if the valves are as bad as you say they are, you really don't want craploads of carbon chunks or chips making their way through the combustion chamber to the exhaust valves.
How do you know to apply the conversion? That's easy! If you live in the USA or Canada, we use PON. If your manual mentions Research Octane Number, you need to convert it to PON. Plus, if you look carefully on the pumps, they tell you what formula they use. Our pumps are labeled with the R+M/2 (PON) nomenclature, typically on a label near the pump handle. If you see that, it's PON but really you don't have to worry unless you're on another continent.