DUMB THING

could it be your throttle cable is wore out or ur kill switch is messed up check wiring to make sure something isnt close to coming unplugged but i would say throttle cable
 
wires ground to the nut that holds your headlight on (1988 - 2002) and if you have a bad wire.. or the piece is broken or something, when you turn it could possibly be trying to push that grounding wire off, which would either kill your motor, or keep it from shutting off...
 
there definately has to be a short somewhere. the reason it doesnt shut off when ur running it hard and turn to the left is b/c the blaster kill switch is incapable of dumping all the power when under full load. my throttle stuck when i was messin with it in the garage one time. turned the switch off, still running wide open, turned off and removed key, still running. pushed the plug wire off, still ran b/c the side of it was touching the plug still and the electricity was actually going thru the rubber. finally just grabbed the fuel line and ripped it off, then dad took a stick and pushed the spark plug wire away from the plug and she shut off.... it was scary, she was pegged for i bet over a minute... thot she was gonna blow.