4000 rpm is high. My personal observation is that clutch engagement speed is around 2000 with the more recent clutches, but I recall having engagement as high as 3000 rpm on leopard clutches several years ago. It might be that your clutch is worn. If so you want to replace it before failure, as the failures can be rather spectacular and damaging.
As for idle, usually that it related to the low speed screw being set too rich on the carb. Be aware, however, that a lean low speed setting for a smooth idle often isn’t the setting you want for actually driving the thing.