Your throttle cables are certainly too tight. For whatever reason. Heck a late dealer of mine had twisted the cables before giving me my ride back. Morons.
Simply bring the handlebars to full right lock while the bike is not running. Observe the throttle and you'll see that the cable is too tight. Look for twisted cables or too tight cables from possible mods made per members discussions above. You can adjust the cable at the handlebar housing, or drastically at the carbs. Thinking 'I have tiny fingers' over and over again will get your hands in that carb area if needed. Or remove the tank...
