7500 FT..WOT..

by Rhett Mitchell in 912 / 914 Technical Questions 10 years ago

Can someone explain the conditions my engine was running under at 7500FT/WOT.
I was maintaining 5500 rpm.
My egt was down, so was I running rich in a lower oxygen atmosphere?
What differences would smaller main jets have made? Better at altitude but leaner at sea level?
I should say, it's a 912ULS.....

Re: 7500 FT..WOT..

by Roger Lee » 10 years ago

Roger Lee

131 5.38k 5.44k

"Better at altitude but leaner at sea level?"

Yes, but

Part of the answer would be based on your personal flying. What elevation is your airport & what is your average flight altitude?
Unless you live and fly at high altitude I would leave it alone. You want to be a little rich at WOT to help prevent detonation. If you fly all the time at higher altitudes then drop the needle one notch and see what happens to the EGT's. This should raise the EGT's some and I'm guessing around 80F.

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

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Re: 7500 FT..WOT..

by Rhett Mitchell » 10 years ago

Rhett Mitchell

8 99 0

Thanks Roger, I'm not saying it's a problem really, just interested in the operating parameters in that situation. I'm getting a fuel flow meter in the future which will be interesting.
I'm based at sea level.
So the needle will affect WOT mixture? Mixture 5000 - 5500?
Visually, it looks like it comes "off the needle" at about 5000 as the egt's drop a bit and I was assuming it was just on the main jet at this point and going rich.
I have been dropping the needles one notch in summer.....runs a bit cleaner I think.

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Re: 7500 FT..WOT..

by Roger Lee » 10 years ago

Roger Lee

131 5.38k 5.44k

At WOT the needle isn't really doing anything. It is the main jet.
If you fly 7500' all the time then drop the needle one notch, but keep an eye on the EGT's and temps while at lower altitudes with lower rpm settings. If you change the main jet then special attention would be prudent at lower altitudes. If you got it too lean or got into a detonation situation it would happen before you even knew it and the damage would be done. I have learned and I'm a believer that some gains aren't worth the journey to get there. It could get costly if a mistake was made and the gain would have been very minor at great expense. If you lived and flew at high altitudes then a main jet could help, but you live at sea level.

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

Thank you said by: Rhett Mitchell

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