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O-470L Idle RPM

Narwhal

PATRON
ANC
Can anyone tell me what RPM an O-470L is supposed to idle at (assume sea level, standard 15C 29.92" day)?

Mine idles at about 500 RPM and the engine has quit 3x during landing rollout. It starts sputtering as airspeed decreases after touchdown, and when power is added to turn off the runway, the engine dies. I've grounded the airplane until the problem can be fixed, and am hoping adjusting the idle to 600-650 rpm might fix it.

For some reason, it runs OK at idle during the runup, even with carb heat on, but after the engine has run for a bit (and heated up?), it tends to sputter and die like this after landing. It has happened with both carb heat on and carb heat off, with outside temps ranging from 5F to 35F. Mixture is always rich and prop forward for landing. It's a C182B with an 82" McCauley 2 blade propeller.

We are trying to rule things out before looking at the carburetor but this is the first step. Carb and engine was overhauled 10 years and 500 hours ago with the rest of the motor. The mags just got their 500 hour insepctions/refresh.

Thanks!
 
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Sounds like it may be running rich. After it quits and the you go to restart it do you have to hold the throttle open to get it to fire back up or pull the mixture.
 
It starts back up after 3-5 seconds of cranking when it dies, with the throttle cracked for 800-1200 rpm and mixture still rich.
 
If your on wheels I think idle speed is suppose to be about 650 but on floats we like to run down around 500 for slow taxi when docking etc.
When you are running down at 500 the mixture has to be set just right. Too rich and it will load up and stall or to lean and it will stumble when you give it throttle from idle. Once its warmed up and idling you can pull the mixture very slowly in small increments and see if it picks up speed and idles nicely then you know your mixture is set to rich. Was it always idling at that speed with no stalling in the past?
 
Sorry I didn't describe that very well. Not in the air. Just warm it up real good on the ground with a high rpm run up and do that test. Even if its not warm enough that it will stall if you can get a cleaner nicer idle you will know your idle mixture on the carb needs reset. Its possible its something entirely different but thats the first thing to try.
 
OK, I went out and did some video documentation today to make working with my mechanic easier, but I'll figure I'll arm myself with internet knowledge as well:

NOTE: EGT is in the top left gauge (so don't be tricked when it says 900 the whole time), RPM/tach is the middle upper gauge.

This is after ground running the engine for a few minutes at 1700 RPM. When pulled to idle, the engine just runs at 500 RPM for about 10 seconds, then stumbles and dies. Mixture is rich the whole time (even though I touch it before restarting), and the engine starts right back up as long as I crack the throttle a bit.

This is the same thing with the carb heat on. It gets a bit rough but idles indefinitely at about 525 RPM. Carb heat seems to help, which would indicate a too lean mixture? A few seconds after I turn carb heat off, it stumbles and dies.

RPM rise test when pulling mixture from 1000 RPM to shutdown. No RPM rise as described in this article (which would seem to indicate mixture set too lean?) https://www.aviationconsumer.com/maintenance/carburetor-idle-issues-check-the-mixture-first/
 
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Nice video. Does sound like you are lean. Intake leak possible amongst many other things. My neighbour had the same kind of problem and his carb had come loose so you want to check that out for sure.
 
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