If you are using a conventional set up, ie a gun and air compressor. Most times when a gun spits, the air pressure dropped to low or you have the hair feed on the gun too low. The gun needs pressure to force enough air through the fluid cap to atomize the material. Spitting can also be caused by material viscosity. Too thick, it will be hard to atomize the material. I'm assuming you are using a catalyzed product? If so, be sure you're not working past its pot life where its starting to cure. Conventional guns are tricky, too much air, not enough product you get sugaring. Too much product, not enough air the product won't atomize properly and will spit.

Yes, that's why you have an air regulator at the gun. You should have a fluid valve too. Strike a balance between air and fluid. Some material data sheets will give suggested air settings.