Two speeds often have trouble on hills.. they just dont shift when they should.. depends on the hill's slope, vehicle weight, gear ratio, etc. Not a lot can be done to make it climb steep hills better other than sprocket (final gear ratio) changes. Different clutch springs can alter where a bike shifts but that's kinda difficult to do.
Idle should be set only when the engine is good and hot. If it's adjusted on a cold engine it'll only idle when the engine is cold.
Aside from that, a clean carb.. correct float level, etc matter. And look for vacuum leaks around the intake manifold. (Spray some Starter Fluid around the area.. if the engine responds, there's a leak)