I bought an aluminum senko mold from Delmart.  I melt the plastic as instructed by the directions and pour into the mold.  I use a metal spoon to stir the plastic with.  All of my senkos are coming out of the mold with hollow bodies.  Some are only hollow in sections and some are hollow all of the way through.  Any suggestions?

Pour slow and make sure you top the mold off a couple of times.

Pour 1, wait a few seconds, top off, move to the second, top off, back to first, top off if necessary.

i agree, pour slowly to allow the trapped air to work it's way out.  Tilt the mold slightly if you can, may help the air make it's way to the top and out.

Add a paddle tail on them and sell them as a Hollow Bodied Senko Paddle Tail.

This is VERY common when you get started with pouring.  It's an easy fix.  Over pour your molds.  Don't try to be stingy or pretty with your plastic, just pour it so it almost flows over the sides of the mold.  Then pour the next cavity.  As you pour this cavity, watch the first one...as soon as you see it start to suck in, top it off again.

I had this same problem and it goes away as you mold gets warm.