What's the temp in the room where you are pouring? If the molds are too cold and the first layer cools down too quick, you can also get cold cracks in your baits. If the temp is too hot, the lams will blend. One common way to warm up the mold is to shoot it full, de-mold, and even shoot it full again and de-mold to bring it up to temp. Just like most of life works- once you get your kinks out, you'll have it down as there are so many variables...
The Twinjector paired with the blending block works great when you want a 50/50 bait. The crossmembers attached to it allow for an even pressure with the two injectors versus trying to push down equally on two separate injectors with a blending tip. (just my opinion) When you want more layers than 2, or doing bellies (o.e. Croaker, etc.) the hand poured belly and injected top (and middle like Jim with his sweet 3 colored Croakers) are tough to beat.
