Motorcycles run at higher RPMs and temperatures than cars so using automotive coolant may not be the best option . I myself use Prestone but since my sliders are worn my RPMs are higher at hiway speeds and my Echarm has been getting warmer than it used to . After doing research I will flush out the Prestone and go with Engine Ice which is better suited for motorcycles . Does it leak any coolant ? I have seen some radiator caps go bad and make one run hot . A pressure tester like mentioned above may be a helpful tool for you . What sparkplug are you using ? Is it a carb or EFI ? If a carb have you done a plugchop to look at the color of the sparkplug to get an idea on how the jetting is ? Here is a plug chart
http://www.4secondsflat.com/plug_chart.html