ROTAX Carb Icing

Could someone who has experienced carb icing in a Rotax tell me what it was like. My engine quit yesterday and for no appearent reason. Wind was 12 mph, I was climbing from about 15 feet and it quit at about 100 feet.

Mark, i have not had an engine out on my rotax 582, but a few times on a hot summer morning, when i got on the ground and looked back at the carb's, i could see lots of moisture had formed on the outside where it attaches to the engine, i touched that area, and it felt very cold , just where the water had formed. i think i was close to having a problem, but it did not happen.

Wayne

Ive only had it once on the 582, after a long glide on to the runway at idle. when I touched down the prop stopped.
Ive flown here in cold damp weather and never had a prob, even with the carbs very cold and wet when I shut down.
Had a few of them in on a 447 engined trike though

Hey Mark,
Mine does not ice up. I keep it in a nice warm building. When the weather is nice enough to fly I'm at work.


How was your landing?

Friendly said:

Could someone who has experienced carb icing in a Rotax tell me what it was like. My engine quit yesterday and for no appearent reason. Wind was 12 mph, I was climbing from about 15 feet and it quit at about 100 feet.

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Well, it's better that it quit at 100 feet rather than 15 feet!

Mark, if you were climbing, I would imagine you were at full throttle? That would be a VERY rare condition for ice. I would would first suspect fuel flow problems of some sort. I was shot down once by a fiber type fuel filter that would accumulate moisture and restrict fuel flow.

I would suggest you carefully check your entire fuel delivery system, beggining with the strainer in the tank and follow on thru every part up to and including carb float valves. Be sure your pulse line is not too long and/or too soft. Check your fuel pump istallation to assure the vent hole is down and not blocked. Also be sure your fuel pump is isolated from engine viberations, THAT can shut you down! For fuel filters, I like the big fat cheap ones from the motorcycle shop. Stay away from those little fancy "finger strainer" types or the short disc types.

In other words, I wouldn't waste too much time pondering carb ice unless you find clearer evidence. :noidea:
.

Rotax two-stroke engines tend not to suffer from Carburetor ice, unless you don't give the engine the proper warm-up time before takeoff. There is always some blow-back into the carb from the case, and so long as the case is warm, that will prevent ice buildup.

DennisFetters said:

Rotax two-stroke engines tend not to suffer from Carburetor ice, unless you don't give the engine the proper warm-up time before takeoff. There is always some blow-back into the carb from the case, and so long as the case is warm, that will prevent ice buildup.

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Yes it does .. carb icing is an issue with 2-stroke engines. It may not be as big of a problem as with 4-stroke, but it is a problem. The weakness of the two-stroke engine is air temperature and air density. Rotax has identified 16 reasons for engine failures on two-stroke engines. Every one has been the subject of a Service Bulletin from Rotax to correct these or to educate the operators.

raton

Mark, make sure your fuel pump is not located where it picks up heat from the crankcase. This can cause vapor lock. My first Rotax gyro was subject to this problem until I moved the fuel pump off the case.

Kingchocolate said:

Hey Mark,

How was your landing?

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Any better and I would apply for a patent:first:
Pete,
This is a new filter, put on about 2 hours of flying on it. But it does look black doesnt it? I tried to start the motor after I landed by priming the carbs I pulled the starter about 3 times with no start. When I got home I tried again and it hit the first pull. My electric battery needs replacing as it only shows 11volts. so I pull started my engine that day.
I did not think it was icing because I did not see any sweating on the carbs but the motor runs now, maybe vapor lock is where I need to be looking. Would the engine run hot if it was starving for fuel, high rpms.

Pete , I was running about 6K rpm. But I went about 1/4 mile at 15 feet when I turned and began to climb out. I was about 60 mph when I began the turn and climb
Doug,
I have the pump on the same tube that the engine mounts to. It has 48 hours on the engine in this configuration. I kept the pulse tube short. I pulled the float bowls and they were about 1/2 full of fuel.

helipaddy said:

Ive only had it once on the 582, after a long glide on to the runway at idle. when I touched down the prop stopped.
Ive flown here in cold damp weather and never had a prob, even with the carbs very cold and wet when I shut down.

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I have to agree with Helipaddy, Doug, Dennis and Passing Through. Carby ice on Rotax 2 strokes is very rare. I have only seen it once and that was on a long glide from 7000ft in ideal icing conditions.

Guys,
Engines, 2 and 4 cycle NEVER ice up.

It's the induction systems that Ice up.

On a conventional, carbureted 4 cycle aircraft engine there are 3 sources of "icing"
1) The carburetor's venturi
2) The carburetor's butterfly throttle valve
3) Fuel evaporation (atomization)

All three of the above also require moisture.

The venturi changes the pressure of the incoming air by increasing the velocity and dropping the pressure. The drop in pressure causes a drop in temperature, which can be as much as 90 degrees F.

The now cooler air lowers the temperature of the next object in the airstream, the throttle butterfly valve. If sufficient moisture is present, and the valve is below 32F, icing may occur as the moisture sticks to and accumulates on the butterfly valve.

At idle, the air is forced through a very small opening around the throttle valve. The air has to speed up through this opening and experiences a subsequent temperature drop and loss of temperature. This can also cause ice to form on the valve, especially during long descents with the throttle closed.

The third factor influencing icing is the fuel atomizing in the carb's venturi. Vaporizing fuel lowers it's temperature. The fuel is usually introduced into the carb at the venturi's low pressure area. Downstream from the venturi is the butterfly.

Pop the valve core out of a tire and the escaping air will usually lower the temperature of the valve stem enough to ice up the stem threads (if there is enough moisture around)
Get a little gasoline on your skin and you'll feel the chilling effect of evaporative cooling.
Add them up and you see how they cause induction icing.

If you know your induction system; carburetor, slide carburetor, Posa injector or fuel injection to name a few, take a look at how the air is regulated, where the fuel is "injected" and where the cold air winds up, and you'll see how suseptible your system is to icing!

Tim,
thank you also, it helps my confidence in my Rotax. I have not pulled the filter down yet. It is raining like crazy here again. I have my gyro tied down on a trailer, so when the whether clears, I will pull it out of the shop and run it at 6000 rpm and see if I can duplicate the engine out. If not, I am going to replace everything from the seat out put to the carb inlet. I did have a bigger fuel filter on it in the past, so I will go back to that.

Hey Mark,
Check your fuel source. One time in Alexandria I filled my truck up at a shell station and immediately after I started having problems with it. The next day brought it to the shop. $600.00 dollars to clean my fuel system out. The fuel they poured out of the tank was black.
Shell said it was no way that came from their store. They supposedly test all their fuel.

Mark check your fuel pump the chamber where the pulse line hooks up is prone to build up moisture from the heat of the engine

Kingchocolate said:

Hey Mark,
Check your fuel source. One time in Alexandria I filled my truck up at a shell station and immediately after I started having problems with it. The next day brought it to the shop. $600.00 dollars to clean my fuel system out. The fuel they poured out of the tank was black.
Shell said it was no way that came from their store. They supposedly test all their fuel.

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Yes, I know what you mean Scott. I did check the fuel in the carbs and it was clean, I first suspected water in the fuel. Just because my filter is new does not mean it is good. I am going to run the engine and see if it will die out again. Then change the filter. I want peace of mind, that I found the problem. Not that it just went away.

I started the engine this afternoon and it started 1st pull. Warmed it up for 3 minutes and then went to 5500 rpm. I let it run for 15min. My engine out flight was 11 minutes. The motor ran same as always except the temps were up a small amount which is to be expected. I examined the see thru fuel lines and did not see any air or anything unusual. The carbs did sweat and get cold but nothing it does not usually do. I ran both ignition banks and left and right with no problems. I reexamined the fuel supply and it is all clean as well as the float bowls. I examined the wiring to the switch and found nothing unusual. So I guess I willl change out the fuel supply system to be on the safe side.

Hi Mark

Just a thought, one thing that most who run two strokes engines are aware of is that this type of engine is VERY sensitive to mixture control, and pay very close attention to mixing their gas or the egt if it has oil injection.

However, most also forget the invisible SPOOK called atmospheric pressure or "density altitude" when trouble shooting. Unless one has some form of altitude compensating carbs you can get quite a change in mixture ratio with a major change in barometric pressure, just a thought.

Tony

I still think you need to either replace the fuel pump or take it apart and rebuild it or at least take it apart and inspect it

rotax 618 bing carb ice

rotax 618 bing carb ice

I have had my Rotax 618/bing carbs freeze up during one flight this winter. It was around 29F degrees with wet snow. I noticed the throttle was getting increasingly stiff and eventually froze up- I had to kill the ignition to land- fortunatly, I was close to the airport when the throttle started to lockup so I turned around to the airport. I landed engine-out and removed the air cleaner- there was ice all along the slider inside the carb- a few minuites and the heat from the engine melted it- I went for another short flight without any problems....It origionally took about 25 minutes for them to freeze. I won't fly in wet/cold conditions with getting a carb heater. I have no choice living here in michigan. It is pretty interesting when taking off of a grass runway thats completly ice and snow- no ground direction control at all- I definetly wouldn't recommend that kind of takeoff without a lot of flying hours. Since September of 08, I have flown 57 hours- in everything from 35+ mph gusty winds, snow flurries, light rain, you name it. Only carb ice one time though.

Tony,
I appreciate the input, but most people who know me will tell you I don't get much density change, unless the weather changes. (I have a terrible fear of heights).
John,
I am going to replace the pump and also order the rebuild kit for the one I have now to keep it for a spare.
Snobird
That is quite a story, I don't think landing on Ice is something I want to do. I would like to join the mile high club.