EGT temps

[84KF 4]

Ok..here's the deal.

I have been using Premium auto gas and egt was always 1450 plusminus a few degrees at cruise. Today I put 15 gals. of 100LL avgas into empty tanks and egt runs hotter, 1500 and wanted to climb with increased rpm's. I noticed this about 30 seconds into take-off. Throttling back brought it back down, but application of increased throttle would make it climb again. 

  I circled the field for 15 minutes of so.... oil and cyl temps quite normal, if not lower the usual because we are now into our first cold spell (50 F.)

Is this egt increase a result of 100LL, or do I look elsewhere. Only one probe, just where it should be, and I checked for any induction leakage at that cylinder...none noted.

The engine ran just fine...  as I said, everything as it's been, except for the higher egt reading. All that is "changed" is the type of fuel.

.......which by the way cost me $70.00 for fifteen freaking gallons.  Why I can remember, in the good ol' days when Avgas was........

steve

[akflyer 1427]

I am 4 stroke rotax ignorant...but will ask a question anyway.. Does Rotax have a jetting chart like they do for 2 strokes?  With colder temps we have to go up in jet sizes for 2 strokes or we get real high EGT's...kinda like john has now lol..

If'n ya had infight adjustable, you could have just bumped up a little pitch..infact, if you are planning on sticking with 100ll you should repitch to keep RPM and EGTs under control.

Did you notice an increase in RPMs?

[84KF 4]

I have not run across any jetting charts for 912's.

I do read about others "playing" with jet and needle settings though but my motto has always been " if it's not broke, don't try to fix it".

Perhaps the colder free air temps now require carb adjustments. In the German Argus inverted V-8 there are three jets per carb. Idle, intermediate, and full throttle.... and we would change them according to season to avoid fouling spark plugs. Warmer air would give a richer mixture for a given jet.

Perhaps I am dealing with a simular situation..... colder air, for a given setting,will lean the mixture out.

[akflyer 1427]

I have not run across any jetting charts for 912's.

I do read about others "playing" with jet and needle settings though but my motto has always been " if it's not broke, don't try to fix it".

Perhaps the colder free air temps now require carb adjustments. In the German Argus inverted V-8 there are three jets per carb. Idle, intermediate, and full throttle.... and we would change them according to season to avoid fouling spark plugs. Warmer air would give a richer mixture for a given jet.

Perhaps I am dealing with a simular situation..... colder air, for a given setting,will lean the mixture out.

That is what happens with our 2 strokes....have to run summer jets and winter jets..