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Thread: Hard Starting Cub

  1. #1
    gdrean's Avatar
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    Hard Starting Cub

    My cub is hard to start when it is warm. Seems to start on one cylinder and just fires on one cylinder for quite a while. If I advance the throttle it may catch but more often seems to load up and die. Sometimes a couple of loud backfires accompany the one cylinder running if I fiddle with the throttle. I have tried starting with 1/4 in throttle, one pump, no throttle to no avail. When it is poping on one cylinder, I have tried carb heat, leaning, throttle, to try to get the other cylinders to catch but no dice. Recently I have tried leaving the mixture full lean (not moved from shut down) and while cranking, slowly pushing it in (richening) and it will start when it mixture nob is about 1" from the panel.

    I thought about mags, plug wires, carb, but am leaning towards carb with the lean to rich starting that seems to be working. Once running, it idles fine and power seems normal. The engine is an O-320 wide deck 160 hp that was rebuilt by Ly-Con by the previous owner. Timing was checked at annual 1 month ago.This engine is in my Amphib cub and I really want to get this figured out before I get stuck on a river somewhere trying to get it started before disaster strikes. Any sugestions would be appreciated.

    Thanks,

    Gary
    GDrean

  2. #2
    www.SkupTech.com mike mcs repair's Avatar
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    Impulse coupling clicking always??

    Broken impulse spring/floating timing at start speed..???

  3. #3

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    Have the mags been removed & e-gap checked?

    The newer starters spin the crank faster & this retards the "Starting Timing".

    Slick or Lycoming has a chart showing this.

    I think of it as a "Hung Start".


    You can check for this by advancing timing to about 30 degrees FOR START TEST ONLY.

    Do not operate @ higher power with that setting.


    You could remove Primer nozzles & hook up outside of the cylinder for testing.

    This would show if any Coked up,

  4. #4
    jgerard's Avatar
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    It's very important especially with slick mags to do the 500hr inspections.

    Hot starts for me (no electric hand prop) require that I leave the mix out full lean. Any time I bump the throttle enough to make the accelerator pump squirt or touch the primer it's flooded and is a bitch to start unless I go through the flooded engine start procedure. Are you running auto fuel or 100LL?

    Make sure you're primer system is not leaking. Try opening the throttle after you pull the mixture so as to clear out the cylinders. Remember to pull the throttle back to idle once it quits.

    Check for intake gasket leaks

    What do the spark plugs look like? You need to clean them and test with a multimeter and if the resistance is over 4000 ohms throw them away. Normal resistance should be about 800-1800 ohms

    Jason
    Last edited by jgerard; 08-19-2011 at 11:41 AM.

  5. #5

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    3 Timings :

    1. Magneto/engine - (running)

    2.Static Starting -( dictated by magneto lag angle & e-gap)

    3. Cranking - varies inversely with cranking RPM . A faster crank speed retards the timing,

  6. #6
    gdrean's Avatar
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    Mike, P.o.p., and Jason. Thanks for the replys. I was sure it would be a carb problem. I didn't realize faster cranking retards the timing. I installed a B&C started thinking the faster cranking would ensure better starts cold, which it did, but maybe it also made the hot starts worse. I'll get the Mags off and check/do a 500 hour on them. Interestingly at annual they found leaking intake gaskets and replaced them. I had better check that all is tight. I looked over the prime system pretty good but will check again. I have prime on all 4 cylinders. Jason, I run 100ll av gas.
    GDrean

  7. #7
    Steve Pierce's Avatar
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    Gary, Are they Slick mags? If so do you know how long since the E gap was checked. As others have said that is usually the problem, the points wear which changes the internal timing of the magneto. See it all the time.
    Steve Pierce

    Everybody is ignorant, only on different subjects.
    Will Rogers

  8. #8
    cubunltd's Avatar
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    If it starts on one cylinder that tells me the mags are working. You have ignition. I would definitely check the intake system for leaks. an intake leak causes the fuel mixture to be way too lean to fire. Depending on the severity of the leak the cylinders affected will fire after a certain rpm. Had an engine that did that on two cylinders once. Found intake leaks and that cured the problem.

  9. #9

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    A buddy of mine had same type of problem, now shuts down with mags without leaning if planning to restart while still hot, fires right up every time.

  10. #10

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    If you have slick mags that is most likely the problem Gary, If Bendix check the impluse on the left mag. Do you hear it snap when you pull it through? If not mags then I would say you have induction leaks, look with a flashlight for dark staining where the induction tubes bolt on to the cylinder and also watch for leaks on the primer lines with someone working the primer.

    Dave

  11. #11
    gdrean's Avatar
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    Thanks everyone for the replys. Yes, I have Slick mags. I won't be able to check the plane until September. It is in Sandpoint, Id. and I can't get back up there for a couple of weeks. I will check all of the suggestions above and report back.

    Thanks again,

    Gary
    GDrean

  12. #12
    nutter3's Avatar
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    Quote Originally Posted by Douten View Post
    A buddy of mine had same type of problem, now shuts down with mags without leaning if planning to restart while still hot, fires right up every time.
    Great advice Douten. Our -14 was real hard to start when hot, needing alot of cranking and priming. I shut down on the mags yesterday. When I restarted it a couple minutes later, it fired right up! Thanks

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