My simple tip is that you are trying to cast with it like you cast with a fixed spool reel.
Multipliers are totally different and first of all you need to get your head around how different they are.
Using a fixed spool reel is easy, you are casting the weight by holding back the line with your finger and then letting go, very similar to letting go with a bow string or sling shot.
With a multiplying reel, a portion of the forward cast is used to get the spool spinning. And then at the end of the cast your thumb is used to stop the spool spinning.
As you might be aware, mutiplying reels are used on the top of the rod. The best type of reel seat to use with these reels is the pistol grip.
If you are having all sorts of problems with your reel, you need to consult a pro-angler, in the same way that fly fishing beginners go for casting lessons.
It's worth every penny, believe you me.