I have an 1811 and it can be twitchy at times. It's usually is when I start out with my elbow in the air rather than on my right knee. I have found that if I over do it a tad on start up then as the tractor lurches forward , without thinking about my hand pulls back slightly on the go lever and that then makes it jerk forward again. It may not seem like you are doing that but try it with your right elbow on your right knee firmly planted when you start out and see if it helps.
