People in the US run all the OS engines with 10-15% fuel all the time, even in the South where temperatures are about the same as in India. Your nitro content is not the problem. Everything you describe sounds like a lean engine, especially considering that it overheats even with the cowl off. Checking it out with a tach will remove all the guesswork from engine tuning. You can tell if your prop is appropriate to the engine, if your fuel delivery is good enough, if your nose up mix is right, and if you're ok with a low tank. I don't use a tach every time I tune, but I do use one always with initial setup of a plane and whenever I have a problem. It has saved me hours of frustration.