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Thread: Rough running engine when throttled back from full power at circuit height

  1. #11
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    Default Re: Rough running engine when throttled back from full power at circuit height

    Quote Originally Posted by Dan L View Post
    Two things come to mind right away. If the engine has over 500 hours change the spark plug leads. But you’ve done that already.

    Second, have you leaned it aggressively when you throttle back?

    With full rich my O-340 will run rough under those conditions too. Even worse if I pull carb heat thinking it is ice. Leaning is all it takes for me.

    Only test flew the a/c wit the new Coils x 4, Spark Plug Leads x 8 and new Mini-sensors x 2 yesterday late afternoon.
    All went well but need further hours.

    Thanks Charles

  2. #12
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    Default Re: Rough running engine when throttled back from full power at circuit height

    I am having an identical problem, right down to the temp drop in the #1 and #2 cylinders. I too have a 2013 CC-11. Not sure about the carburetor. Happens right as I pull power at the top of the climb out.

    Thanks to all for this very helpful thread!

    -asher

  3. #13
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    Default Re: Rough running engine when throttled back from full power at circuit height

    I think if found the problem! Looks like a service advisory was put out on a subset of carburetors for the CC340. I took the advice of others and had my problem analyzed via Savvy and they were great.

    See attachment for details on the carburetor nozzleN92LG CARBORATOR NOZZEL.pdf

  4. #14
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    Default Re: Rough running engine when throttled back from full power at circuit height

    Quote Originally Posted by Asher View Post
    I think if found the problem! Looks like a service advisory was put out on a subset of carburetors for the CC340. I took the advice of others and had my problem analyzed via Savvy and they were great.

    See attachment for details on the carburetor nozzleN92LG CARBORATOR NOZZEL.pdf
    Asher hi

    My 2013 CC 22 SN 271 has the AvStar carby and consequently I can not use the the improved fuel nozzle for the MS carby as per SB-22. Its a bugger when the manufactures chop and change vendors for critical components like this.

    The new plenum and spacer certainly seemed to have helped. The other issue with the CC 340 is that they - on all accounts from more experienced owners - do run very rich and need to be leaned at the earliest opportunity.

    From SB-22



    <<<Note: The new nozzle is compatible with and may only be installed in MSA carburetors having solid blue epoxy float part number 30-864. Do NOT install the new nozzle in a carburetor equipped with a metal float or any other type float except a solid blue epoxy float. If your carburetor is not equipped with the solid blue epoxy float, part number 30-864, please comply with Marvel-Schebler® service bulletin SB-2. Additionally fuel nozzle 47-862 is NOT approved for use in carburetors manufactured, overhauled, or serviced by AVStar Fuel Systems even where the carburetor model and part number appears to be the same or is similar to the MSA carburetor designation. >>>>

  5. #15
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    Default Rough running engine when throttled back from full power - RESOLVED!!!!

    I just got my carburetor back form AvStar, the replaced nozzles to the #1 and #2 cylinders (I think). Anyway when I described the problem, they immediately knew what the issue was. Unfortunately, they did charge me, even though the problem was a manufacturing defect. Oh well. $400

    That aside, the fix works GREAT. If done several flights now and absolutely no problem. Cylinder head temps are more uniform and as an added bonus there is significantly more power and a noticeably shorter takeoff roll.

  6. #16
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    Default Re: Rough running engine when throttled back from full power - RESOLVED!!!!

    Quote Originally Posted by Asher View Post
    I just got my carburetor back form AvStar, the replaced nozzles to the #1 and #2 cylinders (I think). Anyway when I described the problem, they immediately knew what the issue was. Unfortunately, they did charge me, even though the problem was a manufacturing defect. Oh well. $400

    That aside, the fix works GREAT. If done several flights now and absolutely no problem. Cylinder head temps are more uniform and as an added bonus there is significantly more power and a noticeably shorter takeoff roll.

    Asher hi Thats great news. Who did you deal with at AvStar.
    Do you still lean at circuit height / lower power settings.
    Do you have an engine monitor ?
    I didnt think carburetted engines had nozzles but am not an expert.

    Rgds Charles

  7. #17
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    Default Re: Rough running engine when throttled back from full power - RESOLVED!!!!

    Quote Originally Posted by CharlesTym View Post
    Asher hi Thats great news. Who did you deal with at AvStar.
    Do you still lean at circuit height / lower power settings.
    Do you have an engine monitor ?
    I didnt think carburetted engines had nozzles but am not an expert.

    Rgds Charles
    I do have an engine monitor. Before I had to lean aggressively to to prevent precipitous cooling of the #1 and #2 cylinders and a rough running engine. Now, perfect. Big difference. I was surprised that carburetors had nozzles but apparently this one does, I'm no expert either. But this fix was well worth it! I'm trying to figure out who I dealt with at AVSTAR and I'll post it if I can figure it out. I called their main number and gave them the serial number to the carburetor, they put me through to a gentleman who knew exactly what I was talking about and walked me through arranging the repair.

  8. #18
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    Default Re: Rough running engine when throttled back from full power - PROBLEM RETURNS !!

    Asher hi,

    I had the same problem again today - 5 times in a row.
    Engine ran very rough after throttling back at circuit height (after climb and mixture still rich).
    I leaned it out about 1 - 1.25 inches (roughly) and it still seemed a bit rough, then richened it up (about half an inch in) and it ran better - RPM picked up. Very annoying as it was a perfect evening here.

    Leaning made the engine run better but still not 100% normal.

    So I will contact AvStar tonight - if you happen to recall the name of the person you spoke to at AvStar - let me know.
    Will post the engine data in the morning.

    Rgds Charles

  9. #19
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    Default Re: Rough running engine when throttled back from full power - PROBLEM RETURNS !!

    What RPM do you notice the roughness for you? I used to have issues going through about 2400 rpm. I sent my engine out for IRAN because it was making metal during the prebuy. I had a few SB’s addressed while the engine was out including the intake adapter, and new nozzle (I have the Marvel carb). One other thing John D. From Cubcrafters recommended was having the ignition timing changed to 22.5 degrees. Between the 3 things something seems to have addressed the issue, and I know other people had same symptoms so I’m not sure it was the other things related to IRAN on mine that added to rough running.

    Quote Originally Posted by CharlesTym View Post
    Asher hi,

    I had the same problem again today - 5 times in a row.
    Engine ran very rough after throttling back at circuit height (after climb and mixture still rich).
    I leaned it out about 1 - 1.25 inches (roughly) and it still seemed a bit rough, then richened it up (about half an inch in) and it ran better - RPM picked up. Very annoying as it was a perfect evening here.

    Leaning made the engine run better but still not 100% normal.

    So I will contact AvStar tonight - if you happen to recall the name of the person you spoke to at AvStar - let me know.
    Will post the engine data in the morning.

    Rgds Charles

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