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Thread: Stuttering / sputtering shut down AK4 360 Lycoming

  1. #1

    Stuttering / sputtering shut down AK4 360 Lycoming

    I learned in Cessnas and the standard procedure was to run the engine at about 1500 RPM for 20 or 30 seconds then pull the mixture. It not only shuts down cleaner, but the added benefit is that it cleans the oil from the bottom plugs and gives you a better start next time. I am not sure that 1100 versus 1500 is all that important, but cleaning the bottom plugs after a long taxi in from the runway is a good deal in my opinion.

    ----- Original Message ----
    From: A Lieb <atlieb@gmail.com>
    To: musketeermail@yahoogroups.com
    Sent: Sunday, March 25, 2007 8:41:08 AM
    Subject: [musketeermail] Stuttering / sputtering shut down AK4 360 Lycoming

    Not sure if others experience the continual stutter and sputter on
    shutdown of the engine, but somebody showed me a trick to get a "clean
    shutdown".

    POH says throttle to idle, mixture cutoff, and it would take about 5
    to 7 seconds of coughs and wheezes til the prop finally stoped.

    This past week, somebody suggested to me, instead of throttle to idle,
    to put the rpm at 1000 and then pull mixture. I found that 1100 on my
    engine did wonders and shuts down the engine within 2 or 3 seconds.

    Why is this happen in the first place?

    Do I need an adjustment in mixture settings or is this a normal event
    that I just learned after owning my Sundowner 5 years?

    Allen

  2. #2

    Stuttering / sputtering shut down AK4 360 Lycoming

    There are a couple common causes of the engine not stopping smoothly when you pull the mixture to idle cut off.

    #1) The mixture cut-off valve is worn. The arm that the mixture control
    cable attaches to, comes off, and there is a ~4" long shaft that fits into
    the valve at the bottom of the float bowl. The plug at the end of the
    shaft has worn over the last 30 years, and it leaks a little fuel. That is
    enough to keep it coughing and chugging. Setting the throttle at a higher
    speed makes the air in the manifold more dense, so it requires more fuel
    than the valve can leak, so the engine shuts down smoother from a higher throttle setting.

    #2) The Primer Pump is leaking internally. Could be that the primer isn't
    locked closed, or it could be that the valve that is supposed to seal and
    stop the intake vacuum from being able to suck fuel in past the check
    valves is not sealing well.

    Again, 30+ year old parts.

    Setting the idle mixture has nothing to do with the idle cut-off valve or
    the primer. What you should see is a 10-50 RPM rise in the tach when you pull the mixture smoothly to cut-off from full rich. If you see no rise the idle mixture is too lean. More than 50 RPM and it is too rich.

    The O-360-A4K (or M or J, depending on which model Sundowner you have) is notorious for having an incorrectly set float level in the
    carburetor. This causes the HA-6 sidedraft carburetor to run sloppy rich
    at lower power settings, and this causes rapid plug fouling.

    My suggestion based on years of ownership and repairs is: Start up full
    rich, and then set the RPM to 1000 for warm up. Immediately lean to PEAK RPM. This is usually 1150-1200 RPM. Leave the mixture there until Run up. Upon landing and clearing the active, STOP and set the RPM to 1000, and lean to peak RPM again, and finish all your ground running like this.

    It is amazing how much lead gets on the plugs in just the few minutes after start up and in the few before shut down, when the engine is running over rich and and the power level is at idle or 1000-1200 for ground ops and warm up.

    Bob Steward, A&P IA
    Birmingham, AL

  3. #3

    Stuttering / sputtering shut down AK4 360 Lycoming

    I can't argue whether it is oil, carbon or lead or some combination that fouls the plugs, but they foul and this helps. Your techniques may be a little better than mine, but they don't differ much and any one is better than none, IMHO.

    ----- Original Message ----
    From: A Lieb <atlieb@gmail.com>
    To: WILLIS COOKE <wrcooke@flash.net>
    Cc: musketeermail@yahoogroups.com
    Sent: Sunday, March 25, 2007 12:38:00 PM
    Subject: Re: [musketeermail] Stuttering / sputtering shut down AK4 360 Lycoming

    Surely you mean carbon for the bottom plugs, and not oil????

    The way the ramp is configured at KMBO, 1500 RPM is not an option due
    to prop wash considerations for the plane behind me.

    1100 seems much more acceptable, and I only bump it up to 1100 for
    shutdown purposes.

    Since doing this, have not seen any difference in subsequent startups.

    Allen

  4. #4

    Stuttering / sputtering shut down AK4 360 Lycoming

    >
    > > #1) The mixture cut-off valve is worn. The arm that the mixture control
    > > cable attaches to, comes off, and there is a ~4" long shaft that fits into
    > > the valve at the bottom of the float bowl.
    >
    >I had the engine overhauled ~500 hours ago. Would this have been
    >replaced during this time? It's been this way from get go, before and
    >after overhaul. Are we talking any "safety issues" here?

    This is only on the MA-3 and MA-4 series, the HA-6 side draft has a
    different mixture cut-off. But to answer the question, No, if you didn't
    get a Lycoming Reman or OH, or specifically have the carb OH by Precision
    in Everett WA, then you probably didn't get much in the way of a carb OH at
    engine OH time. Maybe the opened it, cleaned it with a solvent rinse and
    possibly even replaced the throttle shaft if it had play, but anything else
    that didn't fall out BROKEN on the shop floor was unlikely to be replaced
    at engine OH.

    >Only major problem since OH has been the #4 cylinder, valve guide
    >needing overhaul. That was detected at annual, and we sent it off to
    >Holly Springs MS for the overhaul. Compression came back afterwards
    >at 72. Everything else, knock on woodk appears to be up to snuff.

    I like the folks at John Jewell in Holly Springs. They have helped me
    several times.

    > > #2) The Primer Pump is leaking internally. Could be that the primer isn't
    > > locked closed, or it could be that the valve that is supposed to seal and
    > > stop the intake vacuum from being able to suck fuel in past the check
    > > valves is not sealing well. Again, 30+ year old parts.
    >
    >Which brings up another question unrelated to the original post.
    >Primer plunger in the past three flights been very hard to pull out,
    >and more resistant pushing in. The sputtering didn't just start, so
    >insofar as engine performance, no changes. While more difficult
    >priming, I figured to get it looked at in about 8 hours at the next
    >oil change. Any safety issues by waiting or am I sitting on something
    >that should be looked at sooner?

    Probably the primer NOZZLES on the cylinders are stopped up. Remove the
    primer lines, pull the nozzles, and soak them in Hoppes Nitro Solvent from
    your local Gun Shop. Blow them out with compressed air, using a rubber
    tipped air nozzle, and then re-install. I bet it is a LOT easier to stroke
    the primer, and it won't take as many strokes to get the same prime.

    >Fortunately, the POH does say warm up between 1000 and 1200, so I
    >always get it at 1100 and lean slightly, just enough to see the EGT
    >rise, but not agressively. I figure to rather have it too rich then
    >too lean as plugs sure are cheaper then cylinders.

    You can do NOTHING to the cylinders at idle power. Lean until peak RPM and
    have less cylinder/piston deposits.

    >By me shutting down the engine at a higher RPM, am I causing any
    >additional problems of any sorts? Any safety issues here as well?

    No.

    Bob Steward, A&P IA
    Birmingham, AL

  5. #5

    Stuttering / sputtering shut down AK4 360 Lycoming

    >My primer was tough to move in and out.
    >I tried KY Jelly but vaseline worked better and lasted longer.
    >In spite of my previous history, this is no joke... but would be the basis
    >of a good one!
    >Tom Corcoran

    The preferred lube is Parker Fuel Lube. It is a non-fuel soluble "grease".

    Bob Steward, A&P IA
    Birmingham, AL

  6. #6
    Orbiting Earth Orbiting Earth corcoran's Avatar
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    Stuttering / sputtering shut down AK4 360 Lycoming

    My primer was tough to move in and out.

    I tried KY Jelly but vaseline worked better and lasted longer.

    In spite of my previous history, this is no joke... but would be the basis of
    a good one!

    Tom Corcoran

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