[Bruce Edwards]

Sounds like your Dad hit the right setting for your set up. With out a choke it should be a pain to start and keep running when it is cold. All settings should be made with the engine at running temp. With out a choke the fuel mix will be lean when cold. If you try to set it up everything will be off when it warms up.
Playing with the mix screws on ht efront should not have made much of a change how ever the rear ones would as the back side is not open so it will add fuel like it was at idle.
Does that help?