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Carb Icing

  • ajojets
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2 weeks 12 hours ago #23099 by ajojets
Carb Icing was created by ajojets
Hi all, Can anyone on the forum explain how carb icing manifest’s itself on a 912 UL, the other day I had what I would call a misfire pulse that shook the whole aircraft then cleared, about3 or 4 minutes later it did the same again, it did this several times then started running OK.
I have looked at the carbs for debris in the float boats and all OK.
Any ideas or was it just carb icing.
Andy.
( no carb heater fitted)

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1 week 6 days ago #23103 by Bill Hertzel
Replied by Bill Hertzel on topic Carb Icing
Carb ice is caused by the cooling produced as the fuel is atomized in the carburetor.
If the ambient temperature and dew point are within range, the cooling will cause the air in the carburetor to cool below the dew point and the interior walls of the carb will "Sweat".
If the temp and manifold pressure are low enough, the now liquid water will freeze and layer upon layer of ice will begin to build up eventually stopping the engine.
Under the proper conditions, carb ice can happen at ambient temperatures up to 100°F/40°C.

Counterintuitively, High humidity and Low temperature are Not conducive to icing.
Highly Humid Air contains so much water that it is difficult to cause it to freeze.
Low-temperature air does NOT contain much water vapor.

www.boldmethod.com/learn-to-fly/systems/carb-ice/

Bill Hertzel
Rotax 912is
North Ridgeville, OH, USA
whertzel1@yahoo.com
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1 week 6 days ago #23104 by ajojets
Replied by ajojets on topic Carb Icing
Bill, thanks for your reply, I fully understand the causes of icing in the manifold, what I was after was how it affects the 912 engine, I was trying to work out if ice falling from the manifold and into the engine would cause the vibration pulse I was getting every now and then for about 5 or so minutes.
Thanks Andy

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1 week 6 days ago #23107 by Bill Hertzel
Replied by Bill Hertzel on topic Carb Icing
I would think that carb Ice would be more persistent than one miss every few minutes.

What fuel including history, RPM, and MAP were you running.
Kind of sounds like an intermittent "Knock".
Any chance you still have some "Winter Blend" Gas in it?

Bill Hertzel
Rotax 912is
North Ridgeville, OH, USA
whertzel1@yahoo.com
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1 week 5 days ago #23112 by Pacheco
Replied by Pacheco on topic Carb Icing
I agree
Try checking your ignition system, mainly the rotatory ignition key if you have one installed.

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1 week 5 days ago #23113 by ajojets
Replied by ajojets on topic Carb Icing
Hi, I think I’ve found the problem although I don’t know why it should make it misfire,
I decided to change the plugs on pulling one of the bottom plug leads off I found it was just resting over the plug and not pushed home. It must have been making contact most of the time but not all, Not sure why this would cause a misfire as it should have carried on firing on the second plug, any thoughts on why the misfire.

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1 week 5 days ago - 1 week 5 days ago #23115 by DHeal
Replied by DHeal on topic Carb Icing
If one of the two spark plugs in a cylinder is intermittently firing you would surely sense/feel the misfire. The loss of power/efficiency in that cylinder would be noticeable.
Last edit: 1 week 5 days ago by DHeal.

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