I, just like Soilarch, shoot a Predator recurve.
Mine weighs 73lbs @ 29 1/2".
I have a dozen ICS 300`s I shoot from this bow that fly perfectly. They are cut at 31 1/2", with a 50 grain brass insert. Five inch shields. I also have weight tubes in them, with the addition of some automotive silicone squeezed into the point end of the weight tubes. I can`t remember how much silicone I added, but total weight with these arrows is just about 750 grains, with a 175 grain tip.
They fly like carbons, sound like wood, and hit like a freight train.
They ARE stiff for sure, but Predators tend to need a much stiffer shaft than otherwise required. (I think the weight tubes were 8 GPI)
You might want to try removing a weight tube and filling in the last three or four inches of it with some silicone. Squeeze the container slowly with the spout cut to fit inside the weight tube. You can watch the silicone fill in the tube. Keep your grain scale handy and keep weighing it until you have the weight where you want it. Let it dry, re-insert it, and see how it flys.