[edwardc]

If its a Facet fuel pump, another possibility is the (infamous) "stuck ball" problem. The Facet has an internal ball and spring check valve. For some as-yet unknown reason, this ball can become partially or fully "stuck" to its seat when left unused for a longish time.

In the partially stuck position, a small amount of fuel gets by, enough to start and run at idle for quite a while, but quickly dies at higher throttle. In the fully stuck position, it won't even start once the float bowl runs dry.

This spring, I had this happen again at spring commissioning. It's the third time, on two separate Facet pumps, over the course of 8 years.

Fortunately, the diagnostic and short-term fix is quite simple. The bottom of the pump is a bayonet-style twist-off, with a 15/16" nut-shaped boss. Once removed (have a container ready to catch the gas), the bottom of the check valve ball is accessible. Simply press on it gently with a fingertip. It should move up smoothly. If its stuck, a little more force will cause it to break free with a perceptible "click" and then operate smoothly.

Unfortunately, my experience has been that once it starts to stick, it will do so again, the only long-term fix being a new pump.