I have a 1996 25hp Mercury 2 stroke outboard. The carburetor was professionally rebuilt one year ago and the choke solenoid was replaced. I have put 15 hours on it since the work was done. Sometimes the idle speed is too high and it won't come down. Other times the idle speed is fine. Although it is electric start and remote, I only start it with the pull start. I do not have a battery connected. Any ideas what could cause the high idle?