Something else here and I don't see it mentioned is shooting up a pile of bellies and then coming back a week later to top coat them. If you are not using your belly colors immediately after shooting them with the plate, you need to wash them in alcohol to get rid of the natural oils that come out of the plastic when its stored after cooking. You may not feel it but its there and it is NOT product specific. They all do it.

Unless you're going to try and sell a few thousand baits I'd toss that twin injector and or plate and hand pour the bellies using a simple spoon and then injecting right away. I never have the kind of issues you've brought up and that's all I do for 2 color belly shots. Once in a great while on a larger bait I'll use a plate when doing a three color belly shot but not very often.