Idle mixture adjustment
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Tom-D
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More than 50 RPM rise means it is too rich. if it is too rich at sea level, wouldn't it excessively rich at 5k
the short answer to your question is no we don't because the carb has a mixture valve to use when condition dictate.
the short answer to your question is no we don't because the carb has a mixture valve to use when condition dictate.
Tom-D
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They are typically adjusted for home airport.
denverpilot
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They really should be slightly richer here, because they may travel to near sea level. You don’t want to be overly lean if you go land in Kansas after a couple hour flight.
At least one person here thinks mine rises TOO much, but ours rises at least 150 RPM up here. It doesn’t rise that much at sea level.
It may rise 75 there though, which would indicate it needs a tweak toward leaner, but the red knob takes care of it at either elevation just fine and it makes book numbers for fuel burn above idle, so it’s just the idle adjustment that’s a touch rich.
The thing to watch out for if it’s set too rich is carb heat. That’s another knob that’ll make it even richer, and you don’t want it quitting when you pull the carb heat on at low RPM and low airspeed, of course. If it’ll barely run at idle full rich at sea level and carb heat on, it needs a tweak.
The carbed engines are pretty tolerant of being a little out either direction. I’ve seen both too rich and too lean at idle but it’s rare to see it so lean at idle that there’s no RPM rise at all. That’s too far the other way.
Mostly I just move big red knob to wherever the engine runs the smoothest and sounds the healthiest. It’s a slightly different spot on a frigid day than on a scorcher up here, too, with summer DAs pushing the underside 10,000’. And definitely lean as all get out, up at KLXV!
Tom-D
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When understanding the MA3SPA, you must first realize that all fuel leaving the float bowl must go out 1 of two ways. 1 is thru the accelerator pump. and the second and most important is thru the mixture valve.
The idle mixture is the bleed air type, you open the bleed air to lean the mixture you close the bleed to richen the mixture. You have no other control of the idle mixture, other than the mixture valve, idle mixture is mostly controlled by a fixed orifice metering jet you simply control the pressure drawing fuel thru that jet.
The idle mixture is the bleed air type, you open the bleed air to lean the mixture you close the bleed to richen the mixture. You have no other control of the idle mixture, other than the mixture valve, idle mixture is mostly controlled by a fixed orifice metering jet you simply control the pressure drawing fuel thru that jet.
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Dan Thomas
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That's what many POHs will tell you to do, and it's what many pilots don't do. They're afraid of that knob because they don't understand the engine at all. They only know that the engine quits if you pull it out far enough.
I think someone needs some recurrent training. Separate idle feed circuit.
http://www.insightavionics.com/pdf files/MA-4 Carb Manual.pdf
Tom-D
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Exactly,, I make a general statement, That I believe most can understand and some must find fault with it. Typical of a few here.
If you have a seaplane, you set the idle a bit low. Otherwise, you taxi when idling even if you dont want to.
It sounds cool on the ramp too. rubbidda, rubbidda, rubbidda
It sounds cool on the ramp too. rubbidda, rubbidda, rubbidda
There is more than just the title. Try opening the link and READING!
I have given advice and have been challenged on it. I have no problems with defending my POV and accepting others'. Sometimes I learn something, sometimes I provide some helpful advice.
Tom-D
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Thanks,
It would not surprise me if there are some variations in idle mixture adjustment and I believe that...as someone else mentioned, if the idle mixture is adjusted for home field elevation that can make an overly lean mixture when the aircraft does go to a significantly lower altitude airport. I suppose that could result in difficult starting. An option would then be to have a sea level or lower altitude idle mixture adjustment which would result in a higher than 50(or so) rpm rise at the higher altitude airport but could be compensated by the pilot by leaning the mixture more during taxi out to prevent plug fouling.
Perhaps all this has already been stated and perhaps there are some error in what I said(would welcome any corrections). I am just trying to make sure I understand from a pilots point of view about all this.
Appreciate the answers so far.
It would not surprise me if there are some variations in idle mixture adjustment and I believe that...as someone else mentioned, if the idle mixture is adjusted for home field elevation that can make an overly lean mixture when the aircraft does go to a significantly lower altitude airport. I suppose that could result in difficult starting. An option would then be to have a sea level or lower altitude idle mixture adjustment which would result in a higher than 50(or so) rpm rise at the higher altitude airport but could be compensated by the pilot by leaning the mixture more during taxi out to prevent plug fouling.
Perhaps all this has already been stated and perhaps there are some error in what I said(would welcome any corrections). I am just trying to make sure I understand from a pilots point of view about all this.
Appreciate the answers so far.