Results 1 to 29 of 29

Thread: Carb Ice

  1. #1

    Join Date
    Mar 2021
    Location
    Greeley, CO
    Posts
    32
    Post Thanks / Like

    Carb Ice

    Hello,

    Had a couple questions about carb ice. I flew my cub for about 1 year/120 hours with no carb ice problems while taxiing.

    A few weeks ago while heading to the runway my airplane died on me. After messing around figured out it was carb ice. Plane ran fine with carb heat on.

    Questions:
    1. Could something have changed to make it start having problems with carb ice? I don't understand why it "just" started happening. It did happen when temps dropped, but I flew it last winter too with no problems.
    2. With full carb heat on, the aircraft spits and sputters pretty bad at full throttle. If I went full power for a go-around the engine would not run right until I get the carb heat out. Is that normal? I thought carb heat should only cause an RPM drop.

    Any input is appreciated.

  2. #2
    SJ's Avatar
    Join Date
    Jan 2002
    Location
    Northwest Arkansas
    Posts
    16,004
    Post Thanks / Like
    I run carb heat from landing power reduction until short final. Have had the engine die from carb ice more than once at idle. Make sure your carb heat and cabin heat connections are not reversed which can cause too much heat to the carb. Easy to do especially on the Sutton.

    I always put carb heat in on short final because carb heat circumnavigates the air cleaner, and you don’t want to suck stuff up in your carb on the ground.

    sj


    Sent from my iPad using SuperCub.Org
    "Often Mistaken, but Never in Doubt"
    ------------------------------------------

  3. #3

    Join Date
    Mar 2021
    Location
    Greeley, CO
    Posts
    32
    Post Thanks / Like
    Thanks for the info. I'll be checking those heat connections today.

  4. #4
    skywagon8a's Avatar
    Join Date
    Mar 2008
    Location
    SE Mass
    Posts
    12,688
    Post Thanks / Like
    Quote Originally Posted by SJ View Post
    I always put carb heat in on short final because carb heat circumnavigates the air cleaner, and you don’t want to suck stuff up in your carb on the ground.

    sj
    Always a good idea in preparing for a possible go around. Two purposes.
    N1PA

  5. #5

    Join Date
    Mar 2021
    Location
    Greeley, CO
    Posts
    32
    Post Thanks / Like
    It is true that the engine should run fine with carb heat on at full power? It just won't get full RPM right? Mine will barely run at full power with the carb heat fully on.

  6. #6
    skywagon8a's Avatar
    Join Date
    Mar 2008
    Location
    SE Mass
    Posts
    12,688
    Post Thanks / Like
    Quote Originally Posted by n07rosman View Post
    It is true that the engine should run fine with carb heat on at full power? It just won't get full RPM right? Mine will barely run at full power with the carb heat fully on.
    Will it run correctly with the carb heat off? Have you pulled off the heat shroud on the muffler recently? If it's cracked the carb could be sucking exhaust gases with the heat on.
    N1PA
    Likes Richgj3 liked this post

  7. #7

    Join Date
    Mar 2021
    Location
    Greeley, CO
    Posts
    32
    Post Thanks / Like
    Not for very long when it's cold. It gets iced up and dies. When the weather is warm it runs good on the ground with no carb heat. Yes, on the heat shroud. My annual was a few months ago and they honed #4 and put new rings in. I noticed the edges around that shroud are beat up now. Maybe that is why this just started happening. I never had a single problem with this last year and flew all winter.

  8. #8
    skywagon8a's Avatar
    Join Date
    Mar 2008
    Location
    SE Mass
    Posts
    12,688
    Post Thanks / Like
    It's a difficult situation to diagnose from a distance. Have your mechanic pull the drain plug on the carburetor and let it flush out a generous amount of gas. Sometimes some dirt and/or some small amounts of water can accumulate in the carb bowl causing similar symptoms. When dirt/water moves around in the bowl, it creates erratic operation.
    N1PA
    Thanks n07rosman thanked for this post
    Likes jrussl, cubdriver2 liked this post

  9. #9

    Join Date
    Jun 2008
    Location
    TN
    Posts
    83
    Post Thanks / Like
    Quote Originally Posted by n07rosman View Post
    It is true that the engine should run fine with carb heat on at full power? It just won't get full RPM right? Mine will barely run at full power with the carb heat fully on.
    Have you tried leaning the mixture? Carb heat causes a richer mixture. My 180 will spit and sputter with carb heat on and mixture set to full rich. My technique is to select carb heat to cold prior to enriching the mixture on short final.
    Likes Bill.Brine, 68Papa liked this post

  10. #10

    Join Date
    Mar 2021
    Location
    Greeley, CO
    Posts
    32
    Post Thanks / Like
    Yes. Always lean before taxi, then lean for peak performance before taking off. Even when leaned it spits and sputters at full power and carb heat on.
    Thanks mixer thanked for this post
    Likes mixer liked this post

  11. #11

    Join Date
    Oct 2012
    Location
    Posts
    7,952
    Post Thanks / Like
    Draining the carb bowl is good advice. If you have water in the bowl it interrupts fuel getting into the main jet, makes it lean, and carb heat will enrich it and make it run. Catch what you drain to see if you had water. If you're not comfortable doing that, add isopropyl to the fuel and it may help clear the water, but it'll take some time to do so. In fall and winter I use isopropyl as standard practice since I can't sump tanks in sub-freezing temperatures.
    Thanks n07rosman thanked for this post

  12. #12

    Join Date
    Mar 2021
    Location
    Greeley, CO
    Posts
    32
    Post Thanks / Like
    Quote Originally Posted by stewartb View Post
    Draining the carb bowl is good advice. If you have water in the bowl it interrupts fuel getting into the main jet, makes it lean, and carb heat will enrich it and make it run. Catch what you drain to see if you had water. If you're not comfortable doing that, add isopropyl to the fuel and it may help clear the water, but it'll take some time to do so. In fall and winter I use isopropyl as standard practice since I can't sump tanks in sub-freezing temperatures.
    Today it warmed up into the 40's and I went flying. That means if there was water in the bowl it should be gone now right?

  13. #13

    Join Date
    Oct 2012
    Location
    Posts
    7,952
    Post Thanks / Like
    Did you drain it? Water in the bowl doesn’t go away by itself.

  14. #14

    Join Date
    Mar 2021
    Location
    Greeley, CO
    Posts
    32
    Post Thanks / Like
    Quote Originally Posted by stewartb View Post
    Did you drain it? Water in the bowl doesn’t go away by itself.
    No. I thought it would burn through the engine. Guess not.

  15. #15
    skywagon8a's Avatar
    Join Date
    Mar 2008
    Location
    SE Mass
    Posts
    12,688
    Post Thanks / Like
    Quote Originally Posted by n07rosman View Post
    Today it warmed up into the 40's and I went flying. That means if there was water in the bowl it should be gone now right?
    Quote Originally Posted by n07rosman View Post
    No. I thought it would burn through the engine. Guess not.
    Nope!
    It collects in the low spots and sloshes around while the engine is running. This includes small particles of dirt which if allowed to remain can clog the orifices in the carb. It may or may not ever get sucked into the engine. It's an easy job to drain the carb. The plug is at the lower rear of the bowl. Cut the safety wire, take out the plug and let some gas flow. The complete changing of the fuel in the bowl by letting it flow at full force will flush the bowl. It will only take a few minutes to do the job.
    N1PA
    Likes DENNY liked this post

  16. #16

    Join Date
    Oct 2012
    Location
    Posts
    7,952
    Post Thanks / Like
    Here’s a typical aircraft carb. The brass tube is the main jet. Fuel is fed to the jet through the hole in the back. The thing you see next to the hole is the mixture control. It’s a tube with a slot that slips into the fuel port to allow fuel to pass. As the slot is rotated it restricts some of the fuel, leaning the mixture. Very basic. If water gets into the bowl it can displace fuel and interfere with flow to the jet.
    Attached Thumbnails Attached Thumbnails Click image for larger version. 

Name:	4419CA8D-55A7-4C77-AEC4-E51598968E16.jpeg 
Views:	90 
Size:	73.8 KB 
ID:	63545  
    Last edited by stewartb; 11-13-2022 at 05:31 PM.
    Likes wireweinie, JohnnyR liked this post

  17. #17

    Join Date
    Mar 2021
    Location
    Greeley, CO
    Posts
    32
    Post Thanks / Like
    Sounds good. Thanks! I'll get it done.

  18. #18
    BC12D-4-85's Avatar
    Join Date
    Feb 2016
    Location
    Fairbanks, AK.
    Posts
    4,207
    Post Thanks / Like
    I had an O-360 in a PA-12 quit once in winter due to ice in the carb. I pulled the mixture full lean then back rich...it restarted and flew on. Must have crushed the ice blockage at the main jet intake at the top of the pic in #16. A&P didn't drain the carb bowl during recent annual. We drained the carb the next day and ice crystals ran out with the fuel.

    Edit: First pulled carb heat but that didn't fix it. So I moved the mixture off and then on.

    Edit: Checked my logs: In between stop and restart I pumped the throttle and the accelerator pump's discharge would briefly fire the engine so I knew I had fuel in the carb. I then pumped the primer and same result - brief firing - so I knew I had fuel to the gascolator. A&P had adjusted the mixture cable during annual so finally I moved the mixture control to see if it was still connected and it restarted.

    Gary
    Last edited by BC12D-4-85; 11-13-2022 at 11:51 PM.
    Thanks stid2677, JohnnyR, NunavutPA-12 thanked for this post
    Likes DENNY, Brandsman liked this post

  19. #19

    Join Date
    Jan 2007
    Posts
    3,073
    Post Thanks / Like
    Gary
    This is the information that makes reading every post for 10 years worth it!!! That evaluation of the situation is not in any checklist. I don't think it should be, but the process of checking everything and understanding why the piston is pushed down is very important. I don't think I would have tried to adjust the mixture but I will add it to my procedure.
    THANKS
    DENNY
    Thanks BC12D-4-85 thanked for this post
    Likes mixer liked this post

  20. #20
    BC12D-4-85's Avatar
    Join Date
    Feb 2016
    Location
    Fairbanks, AK.
    Posts
    4,207
    Post Thanks / Like
    The rest of the story: I've posted this before but maybe it'll help some others...Did an annual inspection in winter and was parking outdoors at AK28 in below -0 temps. When done with the annual I ran up the engine. The A&P told me much later that it sounded rough but said nothing to me until after the incident above. I went to fly after the annual but a snow storm arrived so I parked the plane but noted a backfire during that post annual runup. A week or two later I flew but noted high EGT and some rough running on takeoff. The engine had higher EGT's for 30-40 minutes then quit. I was at 2000 AGL enroute so had some time to deal with the problem plus had a landing spot under me on skis with a trapper's cabin available. I lost half the altitude getting the plane running. Sometimes our lives are in other's hands so make sure your ride is airworthy.

    It's our owner/operator responsibility to make sure the plane and we are airworthy. Trust but verify.

    Gary
    Likes NunavutPA-12 liked this post

  21. #21

    Join Date
    Mar 2021
    Location
    Greeley, CO
    Posts
    32
    Post Thanks / Like
    Thank you for both of those posts!! Great information. One question....What RPM were you at when you got the icing?

  22. #22
    SchulerJL's Avatar
    Join Date
    Aug 2009
    Location
    Peoria, Illinois
    Posts
    593
    Post Thanks / Like
    About 10 years ago I had serious carb ice issues. Happened quite often, I just got really tired of it. I decided to do the shotgun approach, I had the carb rebuilt, Randy Rubbert rebuilt the carb heat box and I switched from a rectangular air filter to a round with a completely new lower cowl. Problem solved, have not had a problem since - knock on wood. I'm not sure what solved it or what combination but it worked.

  23. #23
    BC12D-4-85's Avatar
    Join Date
    Feb 2016
    Location
    Fairbanks, AK.
    Posts
    4,207
    Post Thanks / Like
    Quote Originally Posted by n07rosman View Post
    Thank you for both of those posts!! Great information. One question....What RPM were you at when you got the icing?
    I ran that O-360 at 2400-2450 where it was smoothest. It first had an 82" Hartzell CS prop, then the proper DFA 82-43 fixed pitch. The installation was Crosswind's design with a very effective airbox and exhaust from a Piper Cherokee (I think). Lots of carb heat and a tight flapper system in the airbox. Fuel was primarily 100LL with an occasional 90 unleaded supreme auto gas. I did all the fueling from a 55 gallon tank with dual fuel filters (regular and a no-go type). If below freezing some ice crystals will pass both of those filters if pumped under pressure...the no-go type only blocks fluid water with its corn starch based element (confirmed with manufacturer).

    I assume there was a slow buildup in the carb bowl of moisture. Then a warm hangar for inspection but no bowl drain, then back out in the winter cold. Preheating may or may not melt any water in the carb depending on temps near the carb. Today I'd drain the carb before winter and if warmed up for maintenance indoors. Also check the rpm rise at idle cutoff to make sure it's correct as air temps change.

    Gary
    Thanks n07rosman thanked for this post
    Likes Bill.Brine liked this post

  24. #24

    Join Date
    Mar 2021
    Location
    Greeley, CO
    Posts
    32
    Post Thanks / Like
    Following up on this thread...We found the entire bowl to be loose. Not just the bolts...but the holes were "wallered" out. You could grab the bowl and wiggle it around. I have rebuilt carb coming and should be back in action soon. Thanks for everyones input. I'll report back if that doesn't fix the problem.

  25. #25
    Gordon Misch's Avatar
    Join Date
    Dec 2003
    Location
    Toledo, Wa (KTDO)
    Posts
    4,177
    Post Thanks / Like
    An element of my preflight is to try to wiggle the air filter, for just that reason. Thanks for the update.
    Gordon

    N4328M KTDO
    Likes Steve Pierce, cubdriver2 liked this post

  26. #26
    BC12D-4-85's Avatar
    Join Date
    Feb 2016
    Location
    Fairbanks, AK.
    Posts
    4,207
    Post Thanks / Like
    This carb bowl being loose causing problems has been mentioned here before. Not sure what starts it or how long it takes to become an issue. I had my MA3-SPA (C-85) overhauled this summer due to a buildup of internal deposits we never could completely drain. I assume when new the gasket (lower fuel bowl to top part) is tight against both mating surfaces. The screws after tightening are safetied by bendable washer tabs so they should stay put.

    So what lets the assembly get loose? Any ideas?

    From the Precision Airmotive MSA 1993 overhaul manual:

    "Install bowl cover screws (2) and safety washers (1) and torque in place 35-45 inch pounds. Bend up a minimum of two tabs on all safety washers." Maybe they need to be checked?

    Gary
    Last edited by BC12D-4-85; 12-07-2022 at 08:50 PM.

  27. #27

    Join Date
    Jan 2007
    Posts
    3,073
    Post Thanks / Like
    I think over time the gasket just continues to compress due the the weight of the air filter and vibration. It can also dry out if it sits for a while oil won't evaporate like gas that is why a lot of other gaskets do OK. I had it happen to my Pacer North of the Brooks range, was a rough flight back at night with smoke and rain and more smoke. I figured it out and tightened the screws. That only lasted a few weeks, a new gasket solved the problem.
    DENNY
    Thanks BC12D-4-85 thanked for this post

  28. #28
    BC12D-4-85's Avatar
    Join Date
    Feb 2016
    Location
    Fairbanks, AK.
    Posts
    4,207
    Post Thanks / Like
    On small 4-cylinder engines Continental adds a triangular support assembly between the forward upper airbox and the lower forward crankcase induction spider mounting stud. It likely helps retain the fuel bowl and suspended air box alignment. Still, checking the carb bowl to throttle assy screws and gasket at annual for tightness might be worthwhile.

    Gary
    Likes DENNY liked this post

  29. #29
    Steve Pierce's Avatar
    Join Date
    Mar 2002
    Location
    Graham, TX
    Posts
    22,350
    Post Thanks / Like
    I torque the bowl screws, let it sit overnight and torque again the next day. Also the same as posted above on pre-flight. Seen the bowl loose several times.
    Steve Pierce

    Everybody is ignorant, only on different subjects.
    Will Rogers
    Likes DENNY, BC12D-4-85 liked this post

Similar Threads

  1. Carb temp port plug on MA4 carb.
    By badmdcnman in forum Tips and Tricks
    Replies: 2
    Last Post: 01-04-2019, 07:39 AM
  2. Need a carb . . .
    By bob turner in forum Cafe Supercub
    Replies: 3
    Last Post: 11-03-2007, 11:57 PM
  3. Carb air box
    By Ralph in forum Super Cub Sick Bay
    Replies: 3
    Last Post: 10-25-2003, 05:38 PM

Bookmarks

Bookmarks

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •