Great starting became hard starting.

Yes, the dieseling is often caused by too far open on the primary throttle. And if you had the primary transition slots exposed at all with the idle setting, that is too far open, and is probably why you lost command of idle mixture with the idle mixture screws. So yes, the primary idle stop was too far open.

The secondary throttle stop should be set by trial and error. It is set to make sure you have a good smooth transition, with no stumble, when you open the throttle enough to start to open the secondaries (which is usually a lot of throttle and RPM). It also effects the air into the engine at idle and very small primary throttle openings and thus effects off-idle transition stumbles, etc.

The common initial setting of this secondary stop is for the bottom end of the secondary transition slots being exposed enough to expose a 'square' shape. But you change it from there as needed for best operation. So if it runs well where you have it, then leave it there. Opening it a bit might help the dieseling; that I don't know for sure.