Also, I've noticed there's an external spring added to assist returning the timing to the retard position. ok, but are you suppose to hold the timing advanced when at higher rpms? Do i need more compression on my control lever to hold it?
The little black screw is to tighten the strip on which the round tabs are mounted. The strip can be positioned so that the round brass tabs are in a suitable position for advance/retard. Possibly also to position it so that the cable doesn't slip out in full advance position.
The external spring assists the returning to ADVANCE position, that's at higher RPMS. I've found the original spring is too strong so my advance control lever wasn't staying in a fixed retarded position at startup. So I've put in a weaker spring. Normally at higher RPMs the external spring is relaxed - you shouldn't have to hold the control lever during riding.
PS I saw some people using the cable slack adjustment to fine-tune timing, but I found that isn't necessary. The coarse setting is the position of the sprocket of the magneto relative to the sprocket on the camshaft. That can be impossible to get into spec, so there are magneto sprockets which have two differently positioned splines which allow rotating on the magneto axis half a tooth. Then the fine tuning is done by slightly adjusting the points gap (0.05mm or so differing from spec).