Engine stumble, Any thoughts?

allowing the fuel mixture to collapse before the new lower
velocity swirl pattern establishes itself... It is a lean stumble in
my book..

Does anyone have a Cessna that does this? or might it be specific to
the Piper/Beech installations? I have never encountered it on my 172M
- and I lean a lot.

On 6 Dec 2005 04:22:14 -0800, "Denny" wrote:

snip for length, not content

Now, if you go full rich mixture for a second, before retarding the
throttle, they do not stumble... If you are leaned out and reduce
throttle at a normal rate they will burble for a second... If you have
been well trained, like my airplane has managed to make me, you
instinctively know to just how fast you can creep the throttle back
through that magic point so there is no stumble when leaned...

Am a flat-lander that hasn't done a lot of hot/high TO's & L's. 99% of
my pattern-to-approach-to-land has been full rich. When learning to
properly manage a TIO-540, lean mixture was typically used during
descent to help keep temps up/rate of change down, but any power
reduction was relatively gradual-and the mixture knobs went to the
panel entering the pattern.

Have time working on/flying in a bunch of carb-d Pipers, but the
Apache is one that I missed out on.

My own pet theory, based on a life time of building - and breaking -
engines is that there is a point where reducing angle of the throttle
plate (butterfly), too rapidly and therefore reducing the air velocity
rapidly, where the existing swirl pattern within the intake manifold
collapses, allowing the fuel mixture to collapse before the new lower
velocity swirl pattern establishes itself... It is a lean stumble in
my book..

I'd buy into that one. Still flat-ass amazes me that a tractor
carburetor works as well as it does. Have been around a bunch of
Archers that stumbled on power reduction going downhill. Again,
mixture ususally full rich, and what I would consider to be a
relatively gradual power reduction. Screwed around with a couple of
them with regard to playing with the mixture, engine relatively
hot/cool, messed with plugs, timing, etc. Were company airplanes not a
customer's, so really wasn't sticking it to anybody, just curious.

Regards;

TC