Fuel Injection flow divider test

04 Oct 2021 Fuel Injection flow divider test

20211001: I have an Airflow Performance FM200 mechanical fuel injection system, and I had thought that it would be a good idea to ensure that the flow to each injector is equal. I did this test before the first flight, and wanted to ensure that all was still ok even at lower throttle/mixture settings, since I saw some roughness on cylinder #1 when on the ground.

I tested 5 conditions to see what the different flows were. Unfortunately I didn’t have a measuring cup so I don’t have the details of how much fuel came out, but I have the following photos from each cylinder to see if they are flowing equal amounts, which is the important part.

• Full throttle, full mixture
• Idle throttle, full mixture
• Full throttle, idle cutoff (ICO) mixture
• Idle throttle, ICO mixture
• 4mm from idle throttle, ICO mixture

As you can see, all the flows are very similar. The photos are on a slight angle, since they were on the wing. All settings flowed fuel, which is a known behavior of the FM200, and one of the reasons that they recommend having the “purge valve” to cut the engine, since the “normal” method of moving the mixture back to ICO does not fully stop the fuel flow.

BTW, the roughness does not seem be happening any more lately – not sure if it’s related to the lower temperatures, or if there was something else causing it like a bit of debris in the flow divider. This test at least showed that the problem is unlikely related to fuel flow.