Richard. Your pour tube may be a little thin and there is no vent on the left. There is a lot of places air could still be trapped. Given there is next to no detail on one half though, I suggest you pour the resin directly into the half with the detail - say pour into the hub and let it flow down the arms and to the rim, to push the air out as it goes. Once done, place the other mould half over that, then secure them together (a sandwich of two thick styrene squares on each side, held by rubber bands. The squares will stop the bands from pulling the edges in and bowing the mould). Tip upright and tap gently to get any air bubble to rise to the top.
When casting wheels, the best way is to make a triangle of .20 thou styrene and cut the tip off with an arc that the wheel fits into. Then glue the base of the triangle to a long length of Styrene square section. That becomes the master. That way, using the sandwich to hold it together, you can squeeze the sides to bellow the mould, pour in one end and let it flow down then up, and it will push out the air. The wide opening of the triangle lets more air out. When the mould is full, stop squeezing and let the sides come together and push surplus resin into the rectangle reservoir:
