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Date: Thu, 22 Mar 2007 00:14:40 -0400
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Subject: carbureted lean-of-peak
From: "bob mackey" <n103md@yahoo.com>
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Thee procedures in the instructions posted by Kevin Kossi
( http://lancaironline.net/lists/lml/Message/40829.html )
don't make much sense to me.
While going from full rich to full lean, every cylinder should
pass through each fuel/air ratio. Each cylinder's peak
EGT will occur when that cylinder's fuel-air mixture is near the
stoichiometric mixture of about 15:1 (air:fuel).
The leanest cylinder is the one that reaches its peak EGT
earliest, or at the highest fuel flow. Not the one that
peaks at the lowest temperature.

Any differences in the maximum EGT are caused by differences
in thermocouples, their placement, compression, or air flow
to the cylinder. It doesn't tell whether that cylinder is leaner
or richer than the others at a given mixture setting.

> H. Repeat paragraphs A through E. on cylinders 2, 3, 4, 5, and 6.
> Now you have established the PEAK EGT for each cylinder. ...
> Now select the cylinder that peaked at the lowest temperature.
> This is the CRITICAL cylinder
> ....

The only way this would make sense is if the variation between
cylinders was primarily due to compression. The one with highest
compression and the greatest risk of detonation, would be the
one with the lowest EGT. At higher compression ratios, more energy
is extracted from the charge during the expansion stroke.
It would take fairly large changes in compression ratio to exceed
the typical variations in thermocouples and their installations.
Sometimes Lycosaurus manufacturing tolerances are sloppy,
but they're not THAT sloppy.

My point is... we probably want to pay attention to *when* the
EGT peaks for each cylinder, rather than the temperature at that
peak. Large differences in peak temperature could be indicative of
other problems, like a bad spark plug, sticky valve, mouse in the
intake, etc.

Or maybe I'm missing something and peak EGT is actually indicative
of which cylinder is leanest. Walter? Care to comment?

Oh and BTW, the richest cylinder is critical when LOP, and the
leanest cylinder is critical when rich of peak.