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Thread: 0320 150 loosing power?

  1. #1

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    0320 150 loosing power?

    HI, I have a super cub 150 and over the last year or so it seems its been loosing power. It used to climb out and around 2500 to 2550 rpm with a borer 80-44. Now I am getting about 2400. about 6-700 ft per min. which I used to see around 1000. It seems to be a coming on gradual. I am thinking it is either the carburetor or muffler. Its only got 400 hours on a penn Yann overhaul.

    Just checking to see if anyone has had this same problem or knows where to start 1st?

    Thanks in advance!

    Scott

  2. #2
    mvivion's Avatar
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    Check the exhaust to be certain baffles haven’t broken and partially blocked exhaust pipe. Does your muffler have the bail?

    MTV
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  3. #3

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    That, and check the ignition timing.

    One of the guys likes to climb out flat, and never noticed. I made a take off to bring it home, and it would not climb. Found both mags worn so far they could not be re-timed. Swing-out engine mount made my job easy.
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  4. #4

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    Also, check that throttle is hitting the stop on carb at wide open
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    Do you have SLICK mags? Do a mag check at 2400 RPM. Make sure the carb bowl is not loose ( air filter moves or blue streaks on carb bowl, big RPM drop with carb heat.) Check everything the others have said.
    DENNY
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  6. #6

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    Quote Originally Posted by mvivion View Post
    Check the exhaust to be certain baffles haven’t broken and partially blocked exhaust pipe. Does your muffler have the bail?

    MTV

    Ok. I will find borescope and check it out. What do you mean by bail? Sorry not a very good mechanic.

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    The mag drop is about 75 on both sides. They are bendix mags
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  8. #8

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    Cam lobes wearing down? Been checking the screen/filter for metal?

  9. #9

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    Where do you live? My first response would be to put some isopropyl fuel additive in. A little drop of water in the carb bowl does what you describe.
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  10. #10
    skywagon8a's Avatar
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    Quote Originally Posted by scottsville View Post
    The mag drop is about 75 on both sides. They are bendix mags
    That is an indication the mag points need to be adjusted. They are no longer breaking at peak E-gap flux.
    N1PA

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    Gordon Misch's Avatar
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    Could you clarify please? I was under the impression that the only drop limit is a max limit. Also, altered point setting will affect mag-to-engine timing, so seems that would be the quick check? I'm interested in your thoughts, thanks.
    Gordon

    N4328M KTDO
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  12. #12
    skywagon8a's Avatar
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    The peak magnetic flux flow through the primary winding of the coils is when the magnet rotation is just coming up on the leading edge of the E-gap. E-Gap is the flat spot where the direction of magnetic field reverses. To get the most power in the secondary winding the points must open at the instant of maximum flux. Over time with the wearing of the points or the cam follower the relationship of the point opening to the maximum flux changes. As this change takes place the spark timing and strength changes/weakens. This changes the timing to the top dead center of the piston and increases the amount of mag drop when you switch one mag off.

    The limit you mention is just that, a recommended limit. 75 rpm drop is higher than it could be when everything is set to optimum. The change from optimum to maximum takes place over time. A perfectly timed mag will have very little drop.
    N1PA
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  13. #13
    wireweinie's Avatar
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    Quote Originally Posted by scottsville View Post
    Ok. I will find borescope and check it out. What do you mean by bail? Sorry not a very good mechanic.
    Take a flashlight and look up the tailpipe. See anything loose? anything that might block the tailpipe outlet? If a bail has been welded on, it will look like two wire arches positioned to keep stuff from covering the tailpipe outlet. If you find ANYTHING that's loose in the muffler, pull it and have it repaired immediately, before further flight.

    Web
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  14. #14
    Gordon Misch's Avatar
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    Pete, I understand the e-gap idea, however 75 is about the drop I've always had at 1800 nominal RPM, including with several iterations of newly overhauled Bendix mags. So seems to me it's about right. That's with external timing right on 25 deg. Thinking a flatter prop might yield less drop? Mine is 82-42.

    Edit: let me re phrase that, ive never seen less than about 75. So dunno what I'm missing?
    Last edited by Gordon Misch; 09-13-2020 at 03:13 PM.
    Gordon

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  15. #15
    skywagon8a's Avatar
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    Gordon, The Bendix manual tells you to set the point opening at a specific angle of the cam. I don't do that. If you set it as I described, then time it to the engine, your mag drop will be lower and you will have a hotter spark. If I had a mag drop as high as 75, I would take the mag off and reset the points. When mine gets up near 60 I start to think about it. I prefer less than 50.
    Checking the mag timing to the engine at the annual and finding a change, is telling you to reset the points timing within the mag. The mag itself hasn't moved in relation to the engine.

    This is the process I use with mags, no matter who made them. They are all the same. All you need is a 1/2" wrench, a screw driver and a piece of paper.

    If your fixing an impulse mag, be certain the fly weights are not engaged.
    N1PA
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  16. #16
    Gordon Misch's Avatar
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    Got it, thanks.
    Gordon

    N4328M KTDO
    My SPOT: tinyurl.com/N4328M (case sensitive)

  17. #17
    BC12D-4-85's Avatar
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    If you're interested in timing and air/fuel versus torque> https://www.cycleworld.com/story/blo...-spark-timing/ Not an aircraft but it does discuss some of the similar factors. His books are a good read for motorhead's.

    Gary

  18. #18
    www.SkupTech.com mike mcs repair's Avatar
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    Pull the plug out of bottom of carb and flush some gas through. Main jet is probably partially blocked by water or debris.

    Check oil screen

    Check fuel screens in carb and in gascolator

    And all the stuff others had mentioned.

    The muffler being blocked you WILL notice a bigger change


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  19. #19

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    There is a bail welded and nothing I can see is loose or in the way!
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  20. #20
    180TigerCub's Avatar
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    Also run a compression check when the engine is warm.
    And it would be a good idea to check the accuracy of your tach.
    How much calendar time is on the engine since overhaul?
    180HP PA-18

  21. #21

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    Quote Originally Posted by 180TigerCub View Post
    Also run a compression check when the engine is warm.
    And it would be a good idea to check the accuracy of your tach.
    How much calendar time is on the engine since overhaul?


    Checked the tach. Its good. Its got about 500 hours since overhaul

  22. #22
    180TigerCub's Avatar
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    Quote Originally Posted by scottsville View Post
    Checked the tach. Its good. Its got about 500 hours since overhaul
    How many years since overhaul?
    180HP PA-18

  23. #23

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    2012 overhauled by penn Yan

  24. #24

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    Have you tried isopropyl alcohol or draining the carb bowl yet? I spent a lot of time and money chasing precisely what you describe only to find about 1/4 tsp of water in the carb. It doesn't go away by itself and it definitely interferes with high power setting fuel flows.
    Last edited by stewartb; 09-15-2020 at 02:57 PM.
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  25. #25
    180TigerCub's Avatar
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    You might have some corrosion but...like the others have suggested, fuel, ignition and compression must all be in place.
    180HP PA-18
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  26. #26

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    I have drained the carb but have not ran it yet. I have not seen any water in the sumps every and I sump before everything flight. but you never know!

  27. #27

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    I'd also inspect the carb heat door and cable. Simple stuff first.
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  28. #28
    www.SkupTech.com mike mcs repair's Avatar
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    Quote Originally Posted by scottsville View Post
    I have drained the carb but have not ran it yet. I have not seen any water in the sumps every and I sump before everything flight. but you never know!
    You may need to blow backwards through main jet then flush again if you got a chunk of something blocking main jet partially......


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  29. #29
    n40ff's Avatar
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    Try leaning. My engine turns 2400 full rich in climb and will increase to 2550 when leaned. I know why mine runs rich(experimental). Anyway worth a try. (Of coarse beingf certified you would want to know why if you have a carb. issue)

    Jack
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  30. #30
    8GCBC's Avatar
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    Lycoming 0-320 Operator Manual, Page 57 Trouble Shooting is a good little bit of interesting information to possibly start looking:

    https://www.lycoming.com/sites/defau...2060297-30.pdf
    2018 R44
    IA/A&P, ATP, SES, CFII, MEI, Rotor PPL (2500 TT)
    http://www.youtube.com/watch?v=SXI48e1heuo
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  31. #31
    skywagon8a's Avatar
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    Quote Originally Posted by 8GCBC View Post
    Lycoming 0-320 Operator Manual, Page 57 Trouble Shooting is a good little bit of interesting information to possibly start looking:

    https://www.lycoming.com/sites/defau...2060297-30.pdf
    Section 6, Pages 6-2 & 6-3
    N1PA
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  32. #32

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    I had a similar problem with my c-90 with a marvel schebler carb suddenly it got worse found the accelerator pump had rust and debris under it and throttle would only open about 1/2 way because of the way the linkage works. Lucky I was able to get off the water and make it home.

  33. #33
    mvivion's Avatar
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    Quote Originally Posted by scottsville View Post
    Ok. I will find borescope and check it out. What do you mean by bail? Sorry not a very good mechanic.
    There is an AD on the stock Cub muffler that requires a wire bail be welded up inside the exhaust pipe to prevent broken baffle pieces from blocking the exhaust.

    if you have other muffler, not required. A bore scope will tell you if there’s junk floating around inside muffler in any case.

    MTV

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    Updates???
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  35. #35

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    Quote Originally Posted by stewartb View Post
    Updates???



    Well I flushed the carb. No change. We ran compression check and the engine was cold. 78-77-78-74 So I don't think it is the engine. Ordered new exhaust system for it and hopefully have a guy coming to check mag timing.
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  36. #36
    skywagon8a's Avatar
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    Quote Originally Posted by scottsville View Post
    ......... hopefully have a guy coming to check mag timing.
    Make certain that he checks the internal timing in the mag, not just the timing of the mag to the engine. Just adjusting the timing of the mag to the engine does not correct the deficiency. If he understands mags, he will know what I speak of. There appears to be many who claim to know, but in reality do not.
    N1PA
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  37. #37
    wireweinie's Avatar
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    Quote Originally Posted by scottsville View Post
    Well I flushed the carb. No change. We ran compression check and the engine was cold. 78-77-78-74 So I don't think it is the engine. Ordered new exhaust system for it and hopefully have a guy coming to check mag timing.
    Just gotta ask. What issue did you find that made you order a new exhaust system?

    Web
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  38. #38
    www.SkupTech.com mike mcs repair's Avatar
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    Quote Originally Posted by wireweinie View Post
    Just gotta ask. What issue did you find that made you order a new exhaust system?

    Web
    that was my thought also.... don't just throw parts at it...

  39. #39
    wireweinie's Avatar
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    Exactly.

    Web
    Life's tough . . . wear a cup.
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  40. #40
    BC12D-4-85's Avatar
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    Hopefully Scott has a source of good maintenance to help figure this loss of power out....like valve timing and lift plus fuel and ignition. Compression is only one component. It takes the rest to produce power. Plus a tach check.

    Gary
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