Engine not shutting down when fuel mixture pull off

[tazin river]

Hello folks

Took our Cessna 180 for a flight yesterday to the cabin and after landing and taxing to the dock the engine did not shut down when I pulled the fuel mixture knob as usual. As I was getting a little too close to the dock, I had to turn the ignition key off...

Same thing occurred on the return trip to town...pulled the mixture control... then engine cough for a while but did not completely stopped and once again had to turn the ignition key off to dock the plane....

Fuel mixture adjustment needed?

Will talk to my AME when he is available but was just wondering if someone else on this site can provide some advices...

Cheers

Bruno

[iflyforpie]

Could be the mixture control. Make sure that it is making both stops... should be easy to see through a cowl flap or exhaust hole in the cowl.

Most likely it's a leaky primer.

[lost in the north]

Check your primer and make sure it's locked.

[tazin river]

oops! That was the problem folks
...unlocked primer that is....

Oh well,

Thanks

[Krimson]

Instead of using your ignition to shut off the engine when mixture ICO will not work, advance the throttle full open. From what I hear, it is easier on your engine.

[iflyforpie]

I don't think that would work very well when docking.. Krimson.

I always used the mags for docking.... mixture always gives a burst of power at the wrong moment (due to rich idle mixture) and takes a few seconds to stop.

[ahramin]

?

How is turning the ignition off hard on your engine?

[iflyforpie]

It leaves fuel in the cylinders, which washes off the oil on the cylinder walls and leaves it unprotected.

The best way to shut down an engine is at about 1000-1200 RPM with the mixture, so the engine will spin longer and throw a fresh coat of oil on the innards.

Of course, when it comes to a choice between that or recontouring the floats... shutting down with the mags is the lesser evil.

[ahramin]

Ah I see the point. In this example though the mixture is already cutoff and the fuel is coming from the primer lines. Would opening the throttle prevent the fuel diluting the oil?

[Krimson]

I don't think that would work very well when docking.. Krimson.

I always used the mags for docking.... mixture always gives a burst of power at the wrong moment (due to rich idle mixture) and takes a few seconds to stop.

Ah, Good point.

[iflyforpie]

Ah I see the point. In this example though the mixture is already cutoff and the fuel is coming from the primer lines. Would opening the throttle prevent the fuel diluting the oil?

To a certain degree... because the engine would quit from being too lean (like blowing a candle out) and the engine would take longer to spin down since it was at a higher RPM... throwing fresh oil on the innards. There would still be fuel leaking out of the primer (rather, being drawn out by vacuum), and on something like a 470, they are above the intake valves so it would drip into the cylinders.

But again... the fuel diluting the oil is a very minor concern in comparison to having a primer that isn't functioning or properly locked.

[Bede]

Iflyforpie,

Interesting point. The float plane I fly I shut off with the mags. When I go to start it it fires up immediately with no prime- easier on the starter IMO. I used to have to hand prop that plane quite a bit so it made that really easy.

[tazin river]

[iIflyforpie,

Interesting point. The float plane I fly I shut off with the mags. When I go to start it it fires up immediately with no prime- easier on the starter IMO. I used to have to hand prop that plane quite a bit so it made that really easy.

Does shutting off the float plane with the mags create a risk of backfire at startup?

Bruno

[lost in the north]

Use the mixture to shut down, once you learn the plane be it fuel injected or a carb it will be easy to start.