I have a small 55 gallon sprayer with a 2 hp B&S engine turning a Hypro 4101 roller pump that i use for weed spraying. The old roller pump went bad, so i replaced it with ta new one that is the same size. My problem is that now the engine dies after the pump begins to build pressure. If i disconnect the spray gun, it runs, as this relieves the pressure. I cant figure out why it is doing this, Any help is much appreciated!