912 slightly rich?

by Rhett Mitchell in 912 / 914 Technical Questions 11 years ago

I belive my 912 ULS is running slightly rich. Main needle clip is on second from bottom (out of 4 notches).
Is this the most common position and is it very common to have different winter/summer settings?
My EGT is about 750/1380 degrees. Plugs are fairly dark but clean.
The exhaust is very black with a powdery soot buildup.

I might drop the needle one notch and see how it goes. Will monitor EGT and plugs......any other signs of too lean?

Re: 912 slightly rich?

by Roger Lee » 11 years ago

Roger Lee

125 5.12k 4.53k

Hi Rhett,

The #3 clip position is normal (third from the top). Your 1380F is not that far off. A needle position move may change the EGT temp about 80F. This can be changed to the #2 position (1 notch higher), but should be done with a few things in mind. Temps can be affected by several things and may not really be off. Plugs, idling too long, flight altitude, prop pitch, air filter, carb sync, ect... can all play a part here. Before you touch the clip I would make sure everything else is okay.

Before starting this make sure your plugs are gapped properly. They should be between .023 - .027. Wider (.027) for hot weather. Change the plugs if they are over 100 hours. Checking plugs after idling will give you a false reading. They may be darker and even have a black dry soot on them. The engine needs to be run at high rpms for 5 minutes and then shut off with no extended idle time. This will help clean up the plugs. Your field elevation and average flight altitude will play a part in your decision. As an example if you live at sea level and only fly at 2K agl then you may want to leave things alone, but if you live at 7K+ and always fly at 10K+ then that will play a part to lean 1 notch with the needle. Make sure your EGT probes are in the right place on the exhaust so you aren't getting an artificial reading. They should be 100mm from the exhaust port. Prop pitch can play a part in your over aircraft temps too. Carb sync if it hasn't been done recently. temps can be affected by one thing or several things as an accumulation.

1 clip position change shouldn't be an issue, but do it for the right reasons and monoriting.

Roger Lee
LSRM-A & Rotax Instructor & Rotax IRC
Tucson, AZ Ryan Airfield (KRYN)
520-349-7056 Cell

Thank you said by: Prof. H. Paul Shuch

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Re: 912 slightly rich?

by Rhett Mitchell » 11 years ago

Rhett Mitchell

8 99 0

Thankyou Roger for your comprehensive reply.
I have a 100 hr sevice next week, so all will be in good order.
I am a sea level to 2000ft flyer as you sugested and with winter approaching I think I will perhaps leave any trial until summer.
Daytime temps often reaching 40/45 degrees C in summer , so perhaps a leaner setting would be more apropriate to trial then.

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912 slightly rich?

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