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Thread: 0-320 starting to run rough over 2000rpm

  1. #1

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    0-320 starting to run rough over 2000rpm

    Long story long

    i wrecked, prop strike etc. fixed plane and built back up exp. installed 10:1 pistons, new ignition harness and champ plugs. That is all I changed on engine. So I fly it the first time running it hard to seat the rings, and I hear/see a 50 rpm 'miss' on the tach. But it does it intermittently. This was in September. When it would do it, it didn't seem to have a specific time, in cruise 2350, climb...off and on. Then go away for say 30 min and do it a few more times. Didn't really think anything of it. So I'm on skis now and have approx 40 hrs since I got it back to together, with it still doing it off and on. One day, I land for 15 min, take off and the thing runs like crap for like 30 solid mins. Wouldn't let me get above like 2200. Backfiring, popping, tach jumping all over. It did seem to get a lil better when I got close to town, but still wasn't right. Pulled plugs, the front 2 bottom were black and wet, the others looked normal. Comp check one in high 60's, rest mid 70's. Tested the new harness, its good. Mag drop is perfect at 1700, and checked it at 2200ish with 75-100 drop.

    Ive tried leaning it way out, running full rich, carb heat doesn't help. I strictly run prem cargas with marvel added religiously. I even put about 10 oz in a tank and almost a qt in the oil at one time to see if it would help, thinking it may be a sticking valve...nothing. And comp check says the valves are seated. Starts fine idles fine, taxis fine etc. but as soon as I break ground and gain rpm-2300 is starts Doin it's 'miss' again'. If I back off to 2000-2100 ish it goes away. engine is a b3b with approx 300hrs since overhaul, same on mags. I currently have mags off and are having them looked at and will install new plugs when I put mags back on(Bendix). It only has ran REALLY crappy one time, other than that it's the miss thing.im hoping mags/plugs will fix it. Im no mech and have been talking to several about the issues. Is it safe to say it's not getting good spark, to light up, then it does and boom backfires? There is black residue in my tailpipe. I've checked ALL the simple stuff. It ran fine before I wrecked and only thing I changed was pistons and the harness....have researched till my eyes have bled. Any ideas appreciated thanks

  2. #2
    skywagon8a's Avatar
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    Start by running a full load of 100LL avgas through it.
    N1PA

  3. #3

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    A few thoughts.

    Did you do a full prop strike inspection on the engine?

    What exhaust are you running? Maybe a loose or failing bale or spark arrestor causing intermittent blockage as it heats up.

    Why auto gas with 10.5:1 compression?

    Old (+30 days) auto fuel can get weird.
    "Don't feed the hipsters"

  4. #4
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    0-320 starting to run rough over 2000rpm

    As I was reading your post I was wondering if you were using Marvel, then I read you were. I tried it once, fouled the plugs frequently so I quit. Flew fine after that. None in oil or fuel. I realise you may have folks say " I've been using this for years". Well maybe so, my engine didn't like it. Also used hi octane car gas for a while, found it backfired a lot when throttling down and lack of response when giving throttle. I would go back to basics, 100 LL and no marvel. I have a standard O360. Maybe you have run this combo for years, maybe something changed in rebuild, maybe it will work again someday, but for now I'd go back.


    Sent from my iPhone using Tapatalk Pro

  5. #5

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    I topped it off with 100ll when I flew it first after it was back together. I have 10:1, and have run 10:1 on several engines with prem car gas, for the exception of prolly a tank every 6 months or so. Yes, prop strike inspection

  6. #6
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    It sounds like either a sticking exhaust valve or a mag problem, with my personal inclination leaning towards a valve.
    After Monday and Tuesday, even the calendar says WTF !

  7. #7

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    Had an identical scenario on a PA-18 with O-320 30 years ago.....turned out to be partially blocked fuel strainers in the fuel tanks restricting fuel flow.

  8. #8

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    Intermittent P lead shorting out? Could be anything but you did have two plugs on one mag fouled while the same cylinder plugs on the other mag were fine. Gotta love intermittents!

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    Might be a little water in the carb bowl. It'll only screw with you when you're at high throttle settings. That little bubble of water won't suck up through the main jet so it bounces around and occasionally restricts the jet. Try draining the carb and check for water. If you use MMO the red dye will bond to water and it's easy to spot. Occasionally adding some isopropyl is a good idea, especially in winter when you can't sump your tanks.

    Be careful adding oil to fuel in the cold. Oil displaces fuel and serves to reduce octane and lean the mixture. Not good in the cold unless your carb is set unusually rich.
    Last edited by stewartb; 01-24-2017 at 10:41 AM.

  10. #10

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    Things that come to mind.
    Do only one change at a time!! . Make sure you talk to the rebuild shop and see if you found a broken tooth or other problem. Mags should be inspected after prop strike, it is often not done but it is not that hard to brake a tooth off or crack something.

    Do not replace plugs until you have tried them with the rebuilt mags, I have had a plug that ran fine below 2100 RPM and cut out above that.

    Did you do a mag check in flight at 2400 rpm? This will pick up a poorly preforming plug/mag (can also scare the piss out of ya when it really runs rough).

    What are your CHT's? High compression pistons run hot and it is pretty easy to accelerate valve wear, I have had a exhaust valve that would intermittently fail to seat at only 500 hours ran like crap when it happened, than cleared and ran fine. At rebuild (not inspection) did it get new jugs or valve guides?

    Drain you float bowl to make sure you don't have any water in it.

    I would say the high rpm miss is from a plug or mag issue. A bad single plug should not cause the prolonged poping, backfire. I would look at a broken mag tooth for that. Could be a valve (do a wobble test). But I will lean to the Mag for this one.

    Keep us posted!!

    DENNY

  11. #11

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    Quote Originally Posted by jkarlovich View Post
    Had an identical scenario on a PA-18 with O-320 30 years ago.....turned out to be partially blocked fuel strainers in the fuel tanks restricting fuel flow.
    Good idea, but nothing was done with tanks before the wreck, and it ran flawlessly before...

  12. #12

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    Quote Originally Posted by DENNY View Post
    Things that come to mind.
    Do only one change at a time!! . Make sure you talk to the rebuild shop and see if you found a broken tooth or other problem. Mags should be inspected after prop strike, it is often not done but it is not that hard to brake a tooth off or crack something.

    Do not replace plugs until you have tried them with the rebuilt mags, I have had a plug that ran fine below 2100 RPM and cut out above that.

    Did you do a mag check in flight at 2400 rpm? This will pick up a poorly preforming plug/mag (can also scare the piss out of ya when it really runs rough).

    What are your CHT's? High compression pistons run hot and it is pretty easy to accelerate valve wear, I have had a exhaust valve that would intermittently fail to seat at only 500 hours ran like crap when it happened, than cleared and ran fine. At rebuild (not inspection) did it get new jugs or valve guides?

    Drain you float bowl to make sure you don't have any water in it.

    I would say the high rpm miss is from a plug or mag issue. A bad single plug should not cause the prolonged poping, backfire. I would look at a broken mag tooth for that. Could be a valve (do a wobble test). But I will lean to the Mag for this one.

    Keep us posted!!

    DENNY
    thought about Doin one thing at a time, but my hangar time is limited, and winching it into the hangar is a pain. So is trying to work on it outside. I figured I'd have spare plugs, if that's not the case, 200-300 bucks won't kill me.

  13. #13

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    Used same cylinders. Just had them honed & re-ringed. Not saying it can't be a sticky valve or spring, but don't see it doing it from day one once I started flying again..it seemed to slowly get a lil worse. I don't know crap about mags but had heard that with strikes it can do damaged internally, which I'm assuming would throw timing outta whack...??

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    Quote Originally Posted by hunt/trapak88 View Post
    thought about Doin one thing at a time, but my hangar time is limited, and winching it into the hangar is a pain. So is trying to work on it outside. I figured I'd have spare plugs, if that's not the case, 200-300 bucks won't kill me.

    no mag check at 2400, as the day it really ran bad, at times I could not get to 2400+....

  15. #15

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    Quote Originally Posted by DENNY View Post
    Things that come to mind.
    Do only one change at a time!! . Make sure you talk to the rebuild shop and see if you found a broken tooth or other problem. Mags should be inspected after prop strike, it is often not done but it is not that hard to brake a tooth off or crack something.

    Do not replace plugs until you have tried them with the rebuilt mags, I have had a plug that ran fine below 2100 RPM and cut out above that.

    Did you do a mag check in flight at 2400 rpm? This will pick up a poorly preforming plug/mag (can also scare the piss out of ya when it really runs rough).

    What are your CHT's? High compression pistons run hot and it is pretty easy to accelerate valve wear, I have had a exhaust valve that would intermittently fail to seat at only 500 hours ran like crap when it happened, than cleared and ran fine. At rebuild (not inspection) did it get new jugs or valve guides?

    Drain you float bowl to make sure you don't have any water in it.

    I would say the high rpm miss is from a plug or mag issue. A bad single plug should not cause the prolonged poping, backfire. I would look at a broken mag tooth for that. Could be a valve (do a wobble test). But I will lean to the Mag for this one.

    Keep us posted!!

    DENNY
    i only have one cht thermocouple on back left jug by exhaust. I can get it above 400 when running it hard(if it'll let me) and how much I've got it leaned. But will drop below 400 in cruise. I have a very basic panel with no Elec, so gauges are minimal.

  16. #16

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    Denny, Joel sture says hi. He's one of my roughnecks...

  17. #17

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    I am still not clear on how much time is on the valves/guides since they have been replaced?
    DENNY

  18. #18

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    I changed mags, plugs, wires, even topped the engine looking for valve problems due to rough running at high rpm....then checked fuel flow to the carburetor which proved insufficient and led me into the tanks. Another expensive lesson for me and checking fuel flow is fairly simple. Could some trash have found it's way into the tanks during repair? The other ideas posted here are all more likely scenarios, but I'd still look at fuel flow based on personal experience.

  19. #19

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    Quote Originally Posted by DENNY View Post
    I am still not clear on how much time is on the valves/guides since they have been replaced?
    DENNY

    Nor am I...not sure on guides/valves. Just know when cylinders were replaced...which I would think came with fresh guts..I've looked back at the engines old logs. No comments on the above..

  20. #20
    nanook's Avatar
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    Sounds like something breaking down in the ignition system, high rpms are when the highest resistance is produced. Look for carbon tracking in distributor caps on mags, coils cracked, arching. Plugs breaking down...

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    Installing new valve guides is not cheap so people usually put that in the logs when they overhaul jugs. I would due some checking to see if it was done. If not you may have more than one problem. Joel can fill you in on my single cylinder CHT rant
    DENNY

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    Quote Originally Posted by DENNY View Post
    Installing new valve guides is not cheap so people usually put that in the logs when they overhaul jugs. I would due some checking to see if it was done. If not you may have more than one problem. Joel can fill you in on my single cylinder CHT rant
    DENNY
    Haha Rodger. I believe they were brand new jugs, not around logs now so can't know for sure. Will cover entire ignition if I have to. If it's not ignition and I have to spend a couple grand fixing this, I may so piss on it and bolt up a 10:1 360

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    It is possible that you have one or more of the "bad" Champion spark plugs that have broken down internally, resulting in high resistance. I'd have my mechanic pull the plugs and run a resistance check on them, replacing any that show high resistance. Newer Champion plugs (finally) are being built the same way as the Tempest plugs that don't seem to experience this problem, so make sure you get "new" (new stock, not new old stock) plugs if you go back to Champion. Myself, I'm done with them, it's Tempest for me from now on...
    Jim Parker
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    Quote Originally Posted by hunt/trapak88 View Post
    Used same cylinders. Just had them honed & re-ringed. Not saying it can't be a sticky valve or spring, but don't see it doing it from day one once I started flying again..it seemed to slowly get a lil worse. I don't know crap about mags but had heard that with strikes it can do damaged internally, which I'm assuming would throw timing outta whack...??
    If you did not O/H or replace the mags after a prop strike, you should have.

  25. #25

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    sounds like carb ice to me. what happens when you pull carb heat when it acting up?

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    had an intake leak that sounded like what you are experiencing. Check intake hoses.

  27. #27
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    An intake leak is unlikely, as they manifest themselves most at low manifold pressure (high vacuum) and have much less effect at full throttle. In effect, they "go away" at high throttle openings. His problem doesn't surface until he gets to a high throttle opening.
    After Monday and Tuesday, even the calendar says WTF !
    Thanks Jonnyo thanked for this post

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    Carb heat does nothing, as in nothing to fix the problem. I'm having a '500 hr' inspection done on mags. I will be buying some rem37by tempest plugs. Heard nothing but bad about champions.

  29. #29
    www.SkupTech.com mike mcs repair's Avatar
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    check mags and make sure all the plastic? internal teeth are still on all the internal gears.... prop strike and cracked teeth do happen, then the jump internal timing...

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    Have checked all intakes, I doubt it

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    Quote Originally Posted by hunt/trapak88 View Post
    Carb heat does nothing, as in nothing to fix the problem. I'm having a '500 hr' inspection done on mags. I will be buying some rem37by tempest plugs. Heard nothing but bad about champions.
    I predict you will like the Tempest plugs. Me, I'll never purchase a Champion again.
    "Don't feed the hipsters"

  32. #32

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    Quote Originally Posted by OLDCROWE View Post
    I predict you will like the Tempest plugs. Me, I'll never purchase a Champion again.
    When I went to OMC outboard motor school I remember the instructor telling us how to "test" spark plugs while performing troubleshooting or a tune up. It's very easy to do: First remove the plugs, carefully set each one on the surface of the water, if it floats re-install in the engine, if it sinks replace it. It's called the "float test" and it seemed to be a highly accurate test for spark plugs.
    Likes lowerchena liked this post

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    I chased issues for weeks on my rebuilt 0-320 w/10:1 pistons. Had some of the same issues. Finally took the advise of an old timer and replaced the carb...bam no issues.

  34. #34
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    Quote Originally Posted by qsmx440 View Post
    ...remove the plugs, carefully set each one on the surface of the water, if it floats re-install in the engine, if it sinks replace it. It's called the "float test" and it seemed to be a highly accurate test for spark plugs.
    Good test for cheap car / motorcycle plugs, for $25 & up aviation plugs not so much.
    Here's a troubleshooting guide from Aircraft Mag Service including how to resistance-test plugs.

    http://www.aircraftmagnetoservice.ne...shooting-guide

    From that webpage:


    • Take an OHM Meter and measure the resistance value from the connection in the bottom of the barrel to the clean center electrode at the firing end, electrode must be bare metal.
    • A new Champion plug will have a value of 800 to 1200 OHMS. New Tempest (formerly Unison-Autolite) will measure 1000 OHMS. Replace any plug above 5000 OHMS.
    • A spark plug bomb tester can test a bad plug and lead you to conclude it is serviceable. The OHM Meter check is simple, readily available, and amazingly accurate in finding misfiring plugs.
    Cessna Skywagon-- accept no substitute!

  35. #35

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    Quote Originally Posted by J5Ron View Post
    I chased issues for weeks on my rebuilt 0-320 w/10:1 pistons. Had some of the same issues. Finally took the advise of an old timer and replaced the carb...bam no issues.
    Thought about carb, but other than possibly re-jetting since I went 10:1(which I've been told by many I don't need to do), it ran fine before I tried flying my cub upside down....if mags/plugs don't fix it that's the next thing I'm gonna look into. The thing ran fine before the mishap, and like I said only thing that changed was pistons/new harness

  36. #36

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    Aero carries tempest plugs?

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    Yes
    DENNY

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    Appreciate ya

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    Holy cow. Not an A&P and never knew so many things could cause a rough running engine. That being said, just watched an 0-320 being worked on for a similar problem with a rough running engine starting at about 1800 rpm. The mechanic was going through the drill checking one thing at a time and before it was over with, he found (on a recent shop overhaul) that one cylinder had the rocker arms reversed (didn't even know that was possible) and in that same cylinder the valve springs were toast (collapsed) due to overheating. Cylinder was overhauled and waiting to be put back on. Have no idea if that will clear up the problem but just throwing that out there as an unqualified pilot that doesn't know much about anything. Sure wouldn't have been anything I would have known to check. Good luck!

  40. #40

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    Quote Originally Posted by st8cop166 View Post
    Holy cow. Not an A&P and never knew so many things could cause a rough running engine. That being said, just watched an 0-320 being worked on for a similar problem with a rough running engine starting at about 1800 rpm. The mechanic was going through the drill checking one thing at a time and before it was over with, he found (on a recent shop overhaul) that one cylinder had the rocker arms reversed (didn't even know that was possible) and in that same cylinder the valve springs were toast (collapsed) due to overheating. Cylinder was overhauled and waiting to be put back on. Have no idea if that will clear up the problem but just throwing that out there as an unqualified pilot that doesn't know much about anything. Sure wouldn't have been anything I would have known to check. Good luck!
    i pulled 3 valve covers off and checked, the exhaust side had the small hole in the bottoms of rocker are the intake had a small dimple lookin hole on the top. I believe that is correct

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