I have 2 plugs - one for the winter and one for the summer. The summer plug minimizes the throttle hang, but in the winter it causes some rough idling until the motor is warm. My winter plug is just slightly (the next drill bit size) bigger, but it makes a big difference for cold starts/idling.
Those copper plugs are less than a $1 at Home Depot - I fooled around with 5 or 6 hole sizes until I found what I like best.
