Re: [T3] Dual Carb Adjustment Procedure

[Adriaan Loedolff <adriaan@eng.uct.ac.za>]

Jim Adney wrote:

> On 28 Sep 2000, at 9:43, Adriaan Loedolff wrote:
>
> > Best economy setting results in the highest EGT and best
> > power occurs at the point where the EGT just begins to drop.
>
> Interesting, but don't these describe the same point? ie, isn't the
> peak also the point where it also starts to drop off, kind of by
> definition? [Assuming a rounded peak, and not a truly flat top,
> which would be rather unnatural.]
>

On piston aero engines the EGT probe is fitted around the exhaust
manifold of the leanest cylinder. (How exactly this is determined I
don't know.) When leaning the mixture the EGT is seen to rise and will
peak somewhere. The exact temperature is not significant as the gauge is
graduated in increments of 25 degrees F. After a peak in EGT, further
leaning results in the engine running rough (this can be quite
pronounced and scary to the unaccustomed pilot!). The mixture is then
enrichened until the engine runs smoothly once more - this is the best
range setting. Further enrichment until a slight drop in EGT occurs
gives the best power setting. The observed peak can be rather flat
depending on air density and the accuracy of the EGT probe & gauge.
These sometimes give inaccurate readings, in fact a fellow pilot once
had the engine cut out on him as he leaned the mixture according to the
EGT gauge! (Passengers don't approve of this....)

Regards

Adriaan Loedolff
'69 Squareback Automatic
Cape Town - South Africa

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