The CS means "cold start" not choke. Gas cars have chokes - restricted air to richen fuel mix. Diesels take 100% air volume that the engine demands...no choke.
The reason the cold start is easier to pull at some times rather than others is because it advances the timing by rotating the camplate rollers. If the camplate is positioned so that the pump is right before or during one of the pressure strokes of the plunger, then by pulling the cold start lever, you will be also pushing the plunger on it's stroke and compressing the plunger return springs. The cold start should also be noticeably easier to pull when the engine is running because the internal pressure of the pump pushes the timing advance piston in the same direction that the cold start pushes it.