83 Evinrude 25 kill switch prob.

[58 Alumacraft]

My 83 Evinrude tiller has problems shutting off, if you push the kill button on the front of the motor at idle it will spit and sputter for at least 5-10 seconds and finally die. If there is just a slight twist on the throttle (increasing the RPM's) it won't even think about shutting down. Is this normal? I have removed the rubber boot on the kill botton and found the contacts to look very clean. Any ideas? Thanks!