As I remember from a few years ago, sometimes the pushrod would wear, so the pump would not get the lift. A quick repair-check was to install washers into the sleeve where the pushrod goes. Effectively increasing the length of the pushrod. Also turn the engine over to make sure the pushrod is going up and down, very little or no movement would indicate a bad camshaft. With the fuel pump off and fuel line hooked up you can work the lever by hand to see if it works (point outlet away from you).