sudden loss of throttle response from idle

[Ina Ditch]

this problem popped up overnight a few days ago. I rode the recon Wednesday night less than a mile and everything was good, I took off work Thursday to ride and found that sudden throttle from idle would cause the engine to bog down to the point it would die. It runs fine at riding rpm's and isn't a problem but sitting in neutral any sudden throttle has the bogging effect.
what is my most likely problem?

Thanks guy's.