There should be a detectable change (small increase) to EGTs if dense air is
causing
the engine to run lean. Or small decreases if carb ice is the culprit.
I've had a recent engine change and find the "new" motor to ice-up during the
start/warm
up processes, much more than the old engine this winter.
Differences in gearbox friction torque may also introduce new affects,
especially
for the 'picky'!
Duncan McF.
> On 31 January 2023 at 14:36 n7188u <chmgarb@gmail.com> wrote:
>
>
>
> Hi Guys (and Gals),
>
> Haven't posted much lately but things going well with my mono. Enjoying it
> more
every day.
>
> One question, and a puzzler for me, regarding engine vibration (yes, I know I
am picky about this subject but I hate when things are running well and then
change):
>
> My new engine (about 70 hrs now) has always ran pretty good. However, as of
> late,
I noticed a slight (emphasis on slight) vibration when I power down to a
low cruise power setting (around 500-5100 RPM). Now, I know that some people
will
start screaming that I should not keep the power that low but I had no issues
with sensing vibration (slight) at that power level before.
>
> Well, I started to suspect that this was happening when the weather got colder
(50s-60s F). EGT looks good at around 1400. And even though I have blocked maybe
1/2 of the oil cooler, it still runs a little bellow 180 (160-170). Coolant
has been as low as mod 150s.
>
> Sure enough, last flight the vibration was noticeable. Yesterday we had a warm
and humid day, in the 80s, so I decided to test my theory. Lo and Behold the
engine ran great. Absolutely no vibration at 5000 RPM.
>
> My suspicion at this point is that the cold air from our ram air induction
> system
is just very cold, and maybe adds a little extra pressure, and the mixture
goes lean with the stock 912S carb setting. # 1 and 2 plugs look normal (slight
tan) but the #3 and 4 look lean (white). Engine is stock as it came from Rotax
with no changes to the carbs made.
>
> If we get a cold day again I will try moving the needles up one notch but I
> wonder
if anyone had an experience like this before.
>
> Best Regards,
> Chris
>
>
>
>
> Read this topic online here:
>
> http://forums.matronics.com/viewtopic.php?p=510082#510082
>
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