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
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