Mixture all the way out, engine keeps running (C150 O200)

Pedals2Paddles

Pedals2Paddles

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Pedals2Paddles
Should pulling the mix all the way out actually cut off fuel on a 150 with an O200? When I pull the mixture at idle, it will continue to run. It is rough and coughing, but continues to run. I have to give the throttle a nudge to make it finally cease and shut down.

I was under the impression that all the way out should be cut-off. Is this not the case? Should I leave it at a certain RPM before pulling the mixture?
 
Somehting needs adjusting most likely. The idle cut-off isn't working. There's a separate idle loop which is what ICO kills. Once you get anywhere near ICO the mixture is so lean that non-idle power settings won't let the engine run.
 
Pedals2Paddles said:
Should pulling the mix all the way out actually cut off fuel on a 150 with an O200? When I pull the mixture at idle, it will continue to run. It is rough and coughing, but continues to run. I have to give the throttle a nudge to make it finally cease and shut down.

I was under the impression that all the way out should be cut-off. Is this not the case? Should I leave it at a certain RPM before pulling the mixture?
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Should be a cutoff. You are correct. That's a maintenance issue that should be addressed ASAP. Stopping the fuel to shutdown keeps a hot mag from starting the engine if somebody moves the prop. Might be a low probability event (bad p-lead, misadjusted mixture AND somebody moves the prop) but it only would take once to ruin your day.

John
 
I agree. Is this by chance like a lawn mower where you just adjust a stop nut to adjust the length of throw? Or similarly simple thing?
 
Pedals2Paddles said:
I agree. Is this by chance like a lawn mower where you just adjust a stop nut to adjust the length of throw? Or similarly simple thing?
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If you have to ask, you need an A&P mechanic. :yes:

This is not a lawn mower so trial and error usually doesn't end well. ;)
 
While the engine should cut off when the mixture is pulled full aft with the throttle full aft, it is often better to shut down from something above zero throttle. I find that shutting down from 1000-1200 RPM works a lot better, and Lycoming specifically recommends that for their engines as part of their spark plug fouling avoidance recommendations although I don't know what Continental has to say about that for your O-200.

BTW, if you shut down from about 1100 RPM, the throttle will be perfectly positioned for the next start (as long as nobody else messes with it in the interim, which isn't a problem on my plane).
 
That reminds me, I've been meaning to put a little paint mark on the throttle stick where it gets 1000rpm. Definitely curious if the O200 has a similar recommendation for shutdown. It does make logical sense.
 
Why don't you just shut it down at 1000rpm, and then not touch it?
 
The way these controls were built, it wouldn't surprise me if the cable sheath/housing slipped or the bolt attaching the wire to the carb slipped or the thing isn't rigged properly. I wouldn't fly till you figure out exactly what's going on here.

Also, while the cowling is off, be sure and check how worn the mixture control wire is. They get worn right where they exit the sheath/housing. Eventually they can break. IIRC there is an AD on some Grumman mixture control wires for the same problem.
 
Needs to b adjusted,that's hy they call it idle cut off.
 
ja_user said:
Why don't you just shut it down at 1000rpm, and then not touch it?
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If you get a cut on your arm, do you stop the bleeding, or just close your eyes and pretend you aren't bleeding?
 
Pedals2Paddles said:
I agree. Is this by chance like a lawn mower where you just adjust a stop nut to adjust the length of throw? Or similarly simple thing?
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No. It is a lever on the carburetor that is pulled to a cast stop on the carb body in the idle cutoff position. It is activated by a control wire held into position by a setscrew that sometimes works its way loose. It is a positive check point on any 100 hour/annual.

But I've got a stupid question. Why do you keep asking these questions about your (apparently new to you) new airplane when you could simply pull the cowl and ask a friendly mechanic to show you the mixture control. Nothing is sophisticated on a One-Filthy.

Jim
 
A gentle pointing-out to casual readers that the comments here are not applicable to all engines. They're certainly applicable to the OP's O-200, and frankly the MAJORITY of aircraft engines, but not all carburetors have an idle cut off feature nor lean far enough that the engine will shut down.

Ron Wanttaja
 
The only other possibility I can think of a leaking manual primer. If the primer is in the "in and locked" position and fuel still passes thru it, the engine would run rich and possibly not stop with the mixture placed in "idle cut off".
 
weirdjim said:
But I've got a stupid question. Why do you keep asking these questions about your (apparently new to you) new airplane when you could simply pull the cowl and ask a friendly mechanic to show you the mixture control. Nothing is sophisticated on a One-Filthy.
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I like to know how the thing I own works. I like to know what is likely the problem and how involved it is. I like to know what we're getting ourselves into, be it a self-repair, a mech supervised repair, or dropping it off at the shop. I do not subscribe to pushing it to shop, saying "Here's the plane, make it work". It's fine that lots of owners do. Nobody says you need to do anything but know enough to fly it. I'm much more of a nerd. So every time something is wrong, I come to the forums and look for advice, educate myself on it first, and go from there.

wanttaja said:
A gentle pointing-out to casual readers that the comments here are not applicable to all engines. They're certainly applicable to the OP's O-200, and frankly the MAJORITY of aircraft engines, but not all carburetors have an idle cut off feature nor lean far enough that the engine will shut down.
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Definitely understood. I separate the "in general" stuff from the specifics.
 
What carb do you have? I'm guessing a Marvel Schebler, and the PN doesn't have a -1 at the end of it, and you have a 1 piece Venturi. Running rich was a by product of adding the 1 piece Venturi (that had smoother flow and less fuel atomization making it require more fuel and run rich). There is a marvel service bulletin for the 'fix' referred to as a 'pepper hole nozzle'. It's a couple hundred bucks and takes 2 hours to install.


-VanDy
 
Pull the cowl, watch the carburetor as someone else pushes and pulls the mixture control - you can't miss it (upper rear) Make sure it travels completely to both stop positions on the carburetor body. If that looks good do as previously suggested and ensure the primer is not leaking.
 
VanDy said:
What carb do you have? I'm guessing a Marvel Schebler, and the PN doesn't have a -1 at the end of it, and you have a 1 piece Venturi. Running rich was a by product of adding the 1 piece Venturi (that had smoother flow and less fuel atomization making it require more fuel and run rich). There is a marvel service bulletin for the 'fix' referred to as a 'pepper hole nozzle'. It's a couple hundred bucks and takes 2 hours to install.


-VanDy
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That problem won't prevent idle cutoff.

And the one-piece venturi and perpperbox nozzle were subjects of airworthiness directives and should have been done. The whole process was a fiasco, and made many engines run poorly. There was a final revision to the last AD that permitted the old two-piece venturi and original nozzle to be reinstalled as long as the venturi was inspected for looseness every 100 hours, but few guys did that.

I know one engine tech who used to dress the three legs supporting the secondary venturi on the one-piece affair and got better performance. The legs were cast with a flat surface facing the airflow, and they messed up the air and turbulated it and caused atomization and homogenization problems. He filed them to an airfoil shape and smoothed the engine.

Dan
 
Pedals2Paddles said:
That reminds me, I've been meaning to put a little paint mark on the throttle stick where it gets 1000rpm. Definitely curious if the O200 has a similar recommendation for shutdown. It does make logical sense.
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A paint mark of the "throttle stick" :rolleyes:

How about just look at the tach?
 
Dan Thomas said:
That problem won't prevent idle cutoff.

And the one-piece venturi and perpperbox nozzle were subjects of airworthiness directives and should have been done. The whole process was a fiasco, and made many engines run poorly. There was a final revision to the last AD that permitted the old two-piece venturi and original nozzle to be reinstalled as long as the venturi was inspected for looseness every 100 hours, but few guys did that.

I know one engine tech who used to dress the three legs supporting the secondary venturi on the one-piece affair and got better performance. The legs were cast with a flat surface facing the airflow, and they messed up the air and turbulated it and caused atomization and homogenization problems. He filed them to an airfoil shape and smoothed the engine.

Dan
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weirdjim said:
I must have missed it. Where does he talk about the mixture control? Or idle cutoff?

Thanks,

Jim
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Gotta read between the lines a little bit. Here's my guess, in more detail. At some time 1 piece Venturi was installed and engine ran poorly at idle. Idle mixture was enriched to compensate, which may have been able to kill it at idle at the time, and now it's bypassing enough to keep it running. OR it's a stromberg and the mixture on it will not kill the engine.


-VanDy

Http://vansflyingservices.com
 
Mine used to do the same when I bought it. When I had the carb changed out the A&P adjusted the idle and the cutoff. It works like it should now.
 
VanDy said:
Gotta read between the lines a little bit. Here's my guess, in more detail. At some time 1 piece Venturi was installed and engine ran poorly at idle. Idle mixture was enriched to compensate, which may have been able to kill it at idle at the time, and now it's bypassing enough to keep it running. OR it's a stromberg and the mixture on it will not kill the engine.


-VanDy

Http://vansflyingservices.com
Click to expand...


Nope. The idle cutoff in the mixture control shuts off all the fuel flow, even that to the idle jets, and the idle mixture control is in the flow downstream from the mixture control valve.

I suspect that the control cable is misrigged and isn't letting the mixture control lever come all the way to ICO. Or the female part of the valve in the float bowl has rotated a tiny bit so that the male, which turns inside it, can't close off the opening.

Dan
 
ja_user said:
Why don't you just shut it down at 1000rpm, and then not touch it?
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Actually, I don't mind that recommendation. The carb needs adjusting, but it will help ensure an easy start next time if it's a short time.

Just stay clear of the prop arc until they fix it.

Sent from my iPhone using Tapatalk
 
Pedals2Paddles said:
If you get a cut on your arm, do you stop the bleeding, or just close your eyes and pretend you aren't bleeding?
Click to expand...

Most of the time I don't notice until it's already stopped.:D

OP, what is your idle running at? Where is your timing set? There are several factors that can cause this, it's usually either a timing issue or a carb/FI issue. First I would go through the full timing procedure from scratch, point setting, check dwell °, the whole 9 yards, that should happen every 100hrs really, but rarely does, most of the time the mag just gets turned a bit to compensate. I kinda doubt that will solve your problem, most likely need to go through the carb and find where the bleed is. One other little thing to check before tearing into the carb though is the primer pump. If the seats are getting worn they can leak under the high vacuum of idle.
 
For crying out loud, people. WHy not wait until the OP checks the most common problem ... a slipped cable. Happens all the time. Having him check timing, pulling and examining the carb ... KISS and BURP.

Jim
 
Pulling the carb is probably beyond what we're going to try doing on our own. It was family-comes-to-town weekend. And spent all day today doing paperwork for work. I might make it to the field tomorrow to check out the cable.

As for the other things besides the cable and linkage, I'm glad to have all that input. It makes me that much more educated on the matter if it has to get rectified in annual soon.
 
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