Engine won’t idle

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Skylane182H

Filing Flight Plan
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Dec 19, 2024
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Skylane182H
I have an O-470 U engine that has 2 hours of 75% break in since a major rebuild after prop strike. Everything that could be overhauled was….re certified case and crank. Overhauled rods, pistons and cylinders, mags and carb.
Yesterday, I pulled up behind another plane waiting for my turn at self serve, pulled the throttle to idle and the engine sputtered and died. I gassed up and performed run up flawlessly but again the engine died at throttle out. Slowly leaning the mixture didn’t help either. An obvious no go.
Any ideas on what this issue might be? We’ll obviously pull the cowlings and check stuff. I’m praying this will be a simple mixture screw fix.
 
Hot engines failing to idle is often a idle mixture setting problem.
 
Two settings to check. Idle stop, and idle mixture setting. Don't stress, very likely one of those two is the culprit. Both are very easy to adjust.

First, get your engine operators manual and look up the correct idle RPM range. Probably 700-750. Also find a diagram of your carburetor and identify the location and adjustment instructions for your idle stop screw and idle mixture adjustment.

With a warm running engine, slowly reduce throttle to the stop. What is your RPM when it dies or begins to run roughly? If RPM is below the correct range, then turn the idle set screw on your carb or fuel servo to increase the RPM. The idle stop screw should be set to prevent you from reducing RPM below the correct range.

If you can't get RPM down to the correct idle range without dying, then enrich the idle mixture setting some and try again. Note that is done with the idle mixture adjustment screw on your carb, NOT the mixture control in your cockpit.

Once you get it running at the correct idle speed, set the idle mixture adjustment on the carb. At idle, very slowly lean your mixture until it stumbles and RPM drops off. You should see a rise of 20-50 RPM just before it stumbles. If the rise is greater than that, lean the idle mixture adjustment. If there is no rise, enrich the idle mixture adjustment.

If none of this helps, get with your A&P to check your mag timing.
 
Last edited:
Skylane182H said:
Yesterday, I pulled up behind another plane waiting for my turn at self serve, pulled the throttle to idle and the engine sputtered and died. I gassed up and performed run up flawlessly but again the engine died at throttle out.
Click to expand...
Carb ice. What were the temp and dewpoint at the time?
 
Skylane182H said:
I have an O-470 U engine that has 2 hours of 75% break in since a major rebuild after prop strike. Everything that could be overhauled was….re certified case and crank. Overhauled rods, pistons and cylinders, mags and carb.
Click to expand...
Have you tried to start and check idle after the engine cooled down?
Is the 2 hours part of a specific break-in procedure like Continental's SIL-012?
On your previous flights, what was the idle RPM set to?
 
Another is how hot the ambient temperature and engine was when you experienced this. If everything was hot: can you confirm that all of the fuel lines were run the exact same way they were before? Chance of vapor lock?
 
Thanks to you all for such expedient replies. I’ll get my A&P to look at the issue this week. I will keep you all informed to progress.
 
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