Pulling mixture does not swiftly stop my engine

I did a long flight the other day and when I got back, the engine was nice and heated up. I have been experiencing an erratic idle after the engine is hot. I was experimenting with adjusting the mixture during idle to see if that would smooth it out, and also played with the boost pump to see if fuel was vaporizing in the lines. I usually shut down the engine with the fuel purge line and that will swiftly kill the engine. This time I decided to pull the mixture to kill the engine. Surprisingly, the engine continued to sputter and idle very slowly even with the mixture all the way out. I tried this again on today's flight after filling up the tanks and taxiing back to the hangar. Here is a video of the idle and then pulling the mixture. It did kill the engine eventually and a bit faster than the previous day, but not nice and swiftly like it should. The mixture arm is hitting the stops, so it isn't a linkage issue. I also did some inflight diagnostics for ignition stress, mixture distribution, and induction leaks. After analyzing the data, everything looks normal there, in fact the mixture distribution among the cylinders is really spot on. The induction leak test also shows no signs of leaks. Ignition also was smooth at LOP and doing a mag check got the correct EGT rises. When I pull back the throttle during approach, I do get a bit of a surging idle at low RPM's. I need to do more investigations to get this figured out and get the idle smoothed out.

Here is a quick video from my iPhone of me pulling out the mixture and you can hear the engine surge and sputter a few times before finally stopping. Click on the picture.



Engine is a Lycoming O-320 with Airflow Performance Fuel Injection with purge valve, 8.5-1 pistons, Dual P-mags.

The Airflow Performance FI system manual states that in idle cut-off a small amount of fuel will continue to flow. This is probably what is happening to your engine. Mine does the same thing.

flyinga said:

The Airflow Performance FI system manual states that in idle cut-off a small amount of fuel will continue to flow. This is probably what is happening to your engine. Mine does the same thing.

Click to expand...

Yep, RTFM...

In case you care:

Read the fine manual.

or as we say in the computer biz to end-users: gortfm (Go read the fine manual)



CC

Mike S said:

Yep, RTFM...

Click to expand...

No, Read The Factory Manual

Install and use the purge valve, the engine quits instantly when it is closed to the flow divider.

Oy! Tough audience Bruce!

Oh the joys of Phase 1. The education continues.
Glad it is expected behavior!

What happens if you shut off boost pump first?

Try that to see if the result is the same?

Try a higher RPM

When I had the Mooney, Lycoming O-360, I found I got a cleaner shut down if I pulled the mixture at about 1200 RPM. With the RV-8, Aero Sport O-375 it doesn't seem to matter.