idle dies

If the carb has a choke, the electric need hooked up or the manual wired open if not in use. If your choke is sorted then is it hanging up on high idle? Are you getting too much fuel? If the throttle cable holding the carb open a tad? Do you have a strong return spring?

Form your description its hard for me to grasp what is going on, are you saying it idles fine in park/neutral then idle speed increased when you put in gear?