How to cure 500 exc flameout problems
Advancing your tps closed throttle value to .640 volts instead of the specified .601 volts will get rid of flame outs. Now I imagine there is a range of voltages that will work, but .640 volts is where I ended up. The jd tuner will usually make it better but not get rid of flameout. Try this for yourself. Pull the cover off of tps, mark position of sensor so you can return it to original position. Loosen torx screw just enough to be able to rotate tps. Start bike, if you have a tuner put it back to recommended settings for idle and low speed. Rotate tps ccw very very slightly. You should notice the engine smoothing out-(if you go to far it will get slightly rougher again) tighten screw -- test ride-- night and day difference. Now to set tps properly here is a link to a tps setting tool.
My tps is set to .640 volts.closed throttle and will still get to 3.8 volts at full throttle, as it should.
You can now chug the engine down to nothing and not fear the flameout. Being a light flywheel it obviously doesn't chug like an rfs, but thats the tradeoff for throttle response and handling.