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Thread: Carb Ice- ENGINE SHUT DOWN

  1. #41
    Crash, Jr.'s Avatar
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    Just out of curiosity who is doing Marvel carb rebuilds these days?
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  2. #42
    fancypants's Avatar
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    I had mine done by Bob Bana at RLB Accessory Service in Addison, IL. Not your typical repair station, as it's run out of his basement. He cracked opened the carb in his kitchen to show me the problem. Old-timer that knows his stuff and doesn't mind sharing his knowledge. He was able to turn it around in a day, which probably isn't typical. He's also done some other work for me in the past - new hoses, mags, etc.

    If he wasn't available I probably would have taken it to Aircraft Systems in Rockford.

  3. #43
    jrussl's Avatar
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    I second the recommendation for Aircraft Systems in Rockford. They did mine a few years ago. Fair price, quick turnaround, and came back looking like new.


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  4. #44
    stewartb's Avatar
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    The only shop I’ve ever used for carbs and mags is Fish Creek Airmotive at Palmer Airport. Perfect every time. Never a need to look elsewhere.

  5. #45
    stewartb's Avatar
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    Quote Originally Posted by fancypants View Post
    I put a brand new Marvel carb on my C90 at last overhaul. Flew it for a couple hundred hours last year without any incidences of carb ice. Had to get it overhauled a few months ago due to some water accumulation and rust in the accelerator pump circuit. After overhaul I'm getting carb ice pretty regularly. Haven't quite figured that one out yet.
    Fascinating. In 2021 I’d expect we’d know more about carb icing. My 0-520 doesn’t make ice. Others I know use carb heat continuously. I don’t get it. I do wonder if fuel flow is related. I’ve never been an aggressive leaner and the only time I’ve experienced ice was in a low power descent where I hadn’t adjusted mixture on the way down.
    Last edited by stewartb; 09-24-2021 at 12:07 PM.
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  6. #46
    fancypants's Avatar
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    Yeah, it's odd. I don't have any indication of an induction leak before or after, so fuel flow/mixture at the carb seems like the only thing that could have changed. I've got a ton of data from the EI engine monitor that I can use to deduce a probable cause. Project for a snowy day.

  7. #47
    stewartb's Avatar
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    Careful what you wish for!
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  8. #48

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    Quote Originally Posted by LMartin View Post
    What type of fuel? I don’t think carb heat would work very well with the engine off, except as alternate air. I have a friend that had very similar happen in a borrowed airplane that the owner had been burning ethanol unleaded in (he tested the fuel after and lots of water settled out). The engine may have swallowed a big enough amount of water to quit. It also restarted and then he needed carb heat, we assumed because the water in the fuel iced in the Venturi easier than fuel without water/ethanol.


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    Av Gas…100LL,

  9. #49
    cubdriver2's Avatar
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    Quote Originally Posted by LMartin View Post
    What type of fuel? I don’t think carb heat would work very well with the engine off, except as alternate air. I have a friend that had very similar happen in a borrowed airplane that the owner had been burning ethanol unleaded in (he tested the fuel after and lots of water settled out). The engine may have swallowed a big enough amount of water to quit. It also restarted and then he needed carb heat, we assumed because the water in the fuel iced in the Venturi easier than fuel without water/ethanol.


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    Ethanol gas would have absorbed the water

    Glenn
    "Optimism is going after Moby Dick in a rowboat and taking the tartar sauce with you!"
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  10. #50
    Lisa Martin LMartin's Avatar
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    Quote Originally Posted by cubdriver2 View Post
    Ethanol gas would have absorbed the water

    Glenn
    It does, then it shakes out.


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  11. #51
    Bill Rusk's Avatar
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    My thoughts

    Continental Engines (C-65, C-90, 0-200, 0-235, etc) all have the intake tubes outside the sump. They will all ice at the drop of a hat. Most POH's for these engines will say something like..."Apply Carb Heat before a reduction in throttle" or something like that.

    Lycoming engines have the intake tubes going through the oil sump so the air is heated somewhat before it goes to the engine. As a result these engines are less likely to ice (not that they won't but somewhat less likely) and the older POH's all say something along the lines of...."Carb Heat, as required"
    The newer aircraft with newer POH's will default to always applying card heat due to a few lawsuits.

    For me..... when I fly a "C" engine..... I always apply carb heat....so I use a CGUMPSS check in which C=carb Heat.... then Gas, Undercarriage, Mixture, Prop, Seatbelts, Safety (= CLEAR, CLEAR, CLEAR)

    When flying a Lyc engine I use it when I feel I need it. I have had LOTS of carb ice instances flying floats in SE Alaska in 50 degree temps and light rain. Landed, go idle, engine quits because I had some ice.

    Another thought for detecting it. Look at where the throttle knob sits on your throttle box at say 2400 RPM. Maybe put a mark there. When flying in icing conditions do an occasional check of where the throttle is. If it is further forward of that mark to hold 2400 RPM you may be iced.

    Also be careful leaning. If you have ice and lean it out a little the engine will pick up a few RPM as you just fixed the fuel/air mixture to accommodate the ice (again.....your throttle position will be further forward as well). But if you have leaned for ice then later introduce carb heat the mixture will initially go too rich then too lean as the ice melts out. The engine may stall, or perhaps even quit in this process. Been there done that.

    StewartB made a good point above. Every engine is different. Some never ice and others get ice very quickly. I spent some time flying a couple of 206's this summer. Both nearly identical FWF. But one was extremely prone to Vapor lock, the other hardly ever. Sometimes this stuff is just black magic.

    Just (perhaps) a little knowledge to put in your bag of tricks.

    Hope this helps

    Bill
    Last edited by Bill Rusk; 09-25-2021 at 03:05 PM.
    Very Blessed. "It's not an obsession, it's a passion"
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  12. #52
    Crash, Jr.'s Avatar
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    Just a small point of correction. Lycomings still have the carburator before the sump so the air passing through the carburator isn't heated beforehand. I think the tendency for Lycomings not to make as much carb ice is due to the carb being attached directly to the warm sump so the carburator gets heated by the heat radiating from the oil sump.
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  13. #53
    stewartb's Avatar
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    I don’t think a carb temp gauge would support that. Lots of Lycomings make ice.

    Pulling carb heat does not lean the mixture.

  14. #54
    Crash, Jr.'s Avatar
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    Fair point. Just seems like the consensus is that 4 cylinder Continentals make more carb ice than 4 cylinder Lycomings. Perhaps this is not the case?

    My experience has been with an A65 that makes ice at the drop of a hat, a C85 that has never had carb ice but has carb heat used religiously and an O-360 that has never had an issue with carb ice. No carb temp gauges installed so no idea if the temp is different. Just an opinion based on extrapolation. The Continental carb ice thing could also be related to the fact that most small continentals use Stromberg carbs that may be more prone to icing.

  15. #55
    stewartb's Avatar
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    We’re all taught that air temp drops as air pressure drops after passing through the venturi. Simple science. We’re all taught carb icing probability is relative to a relationship of OAT and humidity. That said, why don’t fuel injection servos ice up? Probably no venturi required since it doesn’t need to pick up fuel there. I should have stayed in school.
    Last edited by stewartb; 09-25-2021 at 02:59 PM.

  16. #56
    Bill Rusk's Avatar
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    StewartB - you are correct. Thanks for catching that. It initially goes too rich then may go too lean as the ice melts out. Corrected in my post.

    Bill
    Last edited by Bill Rusk; 09-25-2021 at 03:03 PM.
    Very Blessed. "It's not an obsession, it's a passion"

  17. #57
    Crash, Jr.'s Avatar
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    Simple. Because the atomization of the fuel in the venturi cools the carburetor throat and induces icing in carburetors. A drop in air pressure does certainly have a cooling effect but not nearly as much as an effect as fuel atomization.

  18. #58
    skywagon8a's Avatar
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    Quote Originally Posted by stewartb View Post
    We’re all taught that air temp drops as air pressure drops after passing through the venturi. Simple science. We’re all taught carb icing probability is relative to a relationship of OAT and humidity. That said, why don’t fuel injection servos ice up?
    Because the fuel is injected at the intake valve inside the warm cylinder head. The cooling effect of the vaporizing fuel is not in the butterfly/venturi area. There is always the possibility of ram ice accumulating, though this is minimal.
    N1PA
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  19. #59
    BC12D-4-85's Avatar
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    I apologize for the repetition but adding a simple manifold pressure gauge can help detect icing. Requires level flight and steady throttle/rpm to maintain indicated pressure, but will drop before most mechanical tachs will as the throttle plate becomes restricted in my experience. If icing detected apply heat and lean to maintain MP. If chasing rpm with throttle as ice builds pay attention to the normal throttle position required to achieve rpm as noted above in #51.

    Gary

  20. #60

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    Thought I would follow up…was a beautiful day here in Valdez…so decided to fire up…flew nearly two hours, trouble free, carb ice free, engine stumble free…plane ran great and seemed to produce plenty of power…was heading in and I wanted to take a look up Valdez Glacier, so I diverted and headed up the glacier.. ( Mistake #1…that wasn’t in my flight plan that I left with my wife!). I was a couple miles up and could feel a slight rumble in my floor board…pulled carb heat, and for a second seemed better…I decided I better just head on home…then I happened, engine rough, stumbling, coughing…it was bad…pulled carb heat, nothing, messed with mixture, nothing, check mag switches, seemed fine…began it look for what might be the best place to set down on the glacier. Pulled mixture just a bit and carb heat just a bit, reduce power slightly and kept it running…made it home. Anyways, I decided to do a compression check after I settled down…

    #4 was down to 30…
    #1 was down to 60…

    3&4 were 72 and 68 respectively…

    Anyways…I’m down on the ground for awhile until I figure this out!

    if there is one thing I know for certain…don’t deviate from your flight plan….

    Thanks for the input folks!
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  21. #61
    skywagon8a's Avatar
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    Quote Originally Posted by J5Ron View Post
    I decided to do a compression check after I settled down…

    #4 was down to 30…
    #1 was down to 60…

    3&4 were 72 and 68 respectively…
    Where did you hear the air leaking out when you did the test? Could be sticky intake valve stems.
    N1PA
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  22. #62
    BC12D-4-85's Avatar
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    Take a good look at the spark plugs and exhaust outlet too for lean/rich signs? Also peek in the plug holes at the valves when open for something unusual. You had good luck onboard that day.

    Gary
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  23. #63
    stewartb's Avatar
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    A low cylinder doesn’t explain the initial stoppage. It sounds like a fuel problem. Any water in the strainer or carb bowl? Maybe an obstruction in a fuel line? I hope you get it sorted.

  24. #64

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    I’ve spent some time reviewing this in my head…a couple added notes…

    I did notice oil temp start to climb prior to this incident.

    I did check fuel flow after the first incident…both tanks seemed to drain well.

    I did not find any water, in either tank, gascolator, or carb bowl…gascolator screen was clean…

    I do have a header less system, and run the plane on the “both” setting…

    I will next pull the oil filter and check for metal, then pull the suspect cylinder…

  25. #65

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    See post #16 I still think it is a valve problem. A sticky valve will cause the same issue and will make for a lean condition in a cylinder (That is why a 4 cylinder EGT/CHT is worth it weight in gold!! If you have a sticky valve be prepared to pull ALL THE JUGS and fix the problem. If you don't have a 4 cylinder EGT/CHT get one. DENNY
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  26. #66
    skywagon8a's Avatar
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    An intake valve sticking partially open will do what you described. I had the same thing happen in a Comanche with an 0-540. There was a little tiny bit of roughness on runup which I attributed to the fact that I hadn't flown that particular plane before. Maybe 15 minutes later while dodging a snow flurry low over some woods.... the engine went silent.. nothing, then after what seemed like forever it just started purring again. A while later while over an airport, it did it again. One intake valve had stuck open and the compression stroke blew all the fuel mixture back through the carburetor. In my case the lifter broke and jammed into the crank case holding an intake valve off it's seat. You may be more lucky with just a buildup on the valve stems needing cleaning.

    Squirt some Kroil https://www.kroil.com on the valve stems, pull the engine through, squirt some more and let it sit overnight.
    N1PA
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  27. #67
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    Out hunting yotes one day with a friend in a cub like me and he knocks one down and goes to land to pick it up. I was circling overhead and watched his prop stop about 30 feet AGL. Fortunately large wheat field with about 3 inches snow cover. After he gets airborne I asked if he intended to cut his engine at that point - nope it was carb ice with no heat on. Took a swipe at a yote once, missed, gave it the gas and seriously rough engine and going down at 50 AGL in very inhospitable terrain, engine came to life just in the nick of time with application of carb heat. I use carb heat all the time now. Was told Lycoming O-320 didn't make ice - wrong.

  28. #68
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    Have you checked the muffler?

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