Oscillating fuel flow

Daniel Tortolani

Hello everyone, yesterday I tried to perform a Gami lean test on my 79' Turbo Lance II, I used the 65% power setting as Gami recommended and started playing with the mixture control, I could go on either side of the curve (rich or lean) with no problems, but when I tried to do the test I noticed that my fuel flow was oscillating in intervals of 0.1 to 0.4 GPH, since the test requires to use 0.2 GPH intervals I stopped trying, now this oscillation is new, sometimes when taxing and the engine was hot I had a rough idle, so I went and checked that, I found that the 2 lower check valves in the admission were in very bad shape and I replaced them, also found that the magnetic flapper valve in the admission was missing the magnet, got that fixed too, rigged all cables and openings, all looked good at that time, but after take off I now have this oscillating problem that didn't have before, the starting and idle problem are now gone, during flight and suspecting the mechanical fuel pump I switched on the electrical fuel pump, but the results were the same, oscillating fuel flow, would like to know if someone in this forum had a similar problem before or any comments, thanks

Stephen

I have had a very similar problem with another kind of gasoline engine (not on my Cherokee Six but on a 26 KWatt gasoline-powered electrical generator). The problem was accumulated gunk in a fuel line. Just to verify, I blew out the line and the "hunting" of the fuel flow stopped (at least for now). My point is that something could be very seriously wrong, and perhaps that could be determined by monitoring fuel pressure as well as the fuel flow gauge, in a ground run-up. Many mechanics have fuel pressure gauges that can be temporarily put into the fuel circuit since it's a necessary part of setting up a new fuel pump installation.