quick answer (edited because I misunderstood the goal the first time around):

The problem is that you need another column with comparative values, if you want your weights to add up to 2. I don't see why you want your weights to add up to 2, though. The whole point of weight is to determine relationships of elements to each other, isn't it?

So. Let's call the new one "value". The values, in top-to-bottom order, are 4, 2, 3, and 1. Multiply each score by its element's value. Add them all together. That gives you a weighted score for each element, and a weighted total score. Divide weighted element score by weighted total score to get percentage. Multiply decimal value of percentage by 2 to get weights that add up to 2.

(apologies for sloppy phrasing)