I recently had the fuel servo overhauled due to having to lean way back at idle. It was old, and had done a great job. After the second time I received it back from the overhaul company 
it seemed working great. Today however, one of the problems that got introduced at overhaul returned...
When I am at idle and taxiing after returning from a flight, the fuel flow will vary from 4 - 6 gph (on the JPI), and the engine will run rough from being too rich. It is very difficult to pull the mixture back to reduce the fuel flow before hitting idle cutoff. However, when I turn on the elec fuel pump, the fuel flow goes rock solid to 3 gph, and the engine idles fine. Turn off the elec fuel pump, problem reappears.
Any idea of what could be causing the problem? If it were the engine driven fuel pump, would it start failing and somehow cause the fuel flow to go up? Why would turning on the elec fuel pump cause the fuel flow to go down - back to where it should be? This just happened on a flight yesterday, and I haven't had much time to try things or talk with my mechanic. (Note that the engine ran fine for a few flights after the overhaul.)
it seemed working great. Today however, one of the problems that got introduced at overhaul returned...When I am at idle and taxiing after returning from a flight, the fuel flow will vary from 4 - 6 gph (on the JPI), and the engine will run rough from being too rich. It is very difficult to pull the mixture back to reduce the fuel flow before hitting idle cutoff. However, when I turn on the elec fuel pump, the fuel flow goes rock solid to 3 gph, and the engine idles fine. Turn off the elec fuel pump, problem reappears.
Any idea of what could be causing the problem? If it were the engine driven fuel pump, would it start failing and somehow cause the fuel flow to go up? Why would turning on the elec fuel pump cause the fuel flow to go down - back to where it should be? This just happened on a flight yesterday, and I haven't had much time to try things or talk with my mechanic. (Note that the engine ran fine for a few flights after the overhaul.)
