Clean curls work best when you find a weight that is too heavy to pull from arms extended to arms all the way bent with strict form.  To do these right (after you are warmed up and have experimented with a few weights first), you should jump them to the "up" position.  DON'T lean back.  It puts too much strain on the low back.  Can cause injury.  Jump it instead.  Like a hang clean.   

From there, bring it down under complete control, maximizing the eccentric (negative) contraction of the biceps muscles.  It is best if you take 2-4 counts to lower the weight.  Remember, you are much stronger lowering the weight, so take your time.  If you can't lower it under complete control, you'll need to lower the weight.