Carb Ice Question

[VictorBravo]

I am thinking my recent engine failure on takeoff MAY have been caused by carb ice. It is a stretch, but a possibility -

I had flown three touch and go landings, the last one within ten minutes of the engine failure on takeoff. On each touch and go, I used carb heat from downwind abeam all the way to touchdown.

HOWEVER, I had moved the carb heat air scoop form the front cylinder baffle to the oil cooling baffle (in the square hole under the propeller). Since I was running cold oil temps and high cylinder temps, I thought I should start covering the oil cooling opening to raise the oil temps and hopefully cool the cylinder temps (keeping less high pressure air from going into the lower cowl). On the last test flight I had over 80% of this square opening taped off. The result was still 165F oil temps. But there was definitely LESS airflow available to the carburetor heat air scoop because of my taping off the oil cooling hole.

HOWEVER, the airplane ran perfectly and did not suffer any known carb icing on the three previous touch and goes in the same configuration (oil hole 80% taped).

After the third touch and go, I parked the airplane in the runup area for about ten minutes while I made an adjustment to the cowl. So the warmth of the engine soaked through the carburetor for a few minutes. The engine restarted normally, I taxied out to the runway and started takeoff, when the engine RPM suddenly dropped off as though I ran out of fuel.

After I stopped the airplane in the dirt next to the runway, it started up fine, idled for a couple of minutes, and quit while idling.

I pushed it to the tiedown and repeated the startup, and it quit again in a few minutes.

A local T-craft owner and IA mechanic came over while it was running the third time, and unlatched the primer, and it ran rough but did not quit.

I taxied it back to the other side of the airport, and in front of my hangar did a full throttle runup for ten seconds, with no problems whatsoever.

The flexible fuel line was not broken or filled with debris. The gascolator was clean. The fuel in the airplane had no water. I had at least 4 gallons in the tank.

Does this sound like it could possibly be carb ice to anyone? Could I have built up some carb ice in the three touch and goes that stayed in ice form for ten minutes of a warm parked airplane, then caused an engine failure on takeoff, then three more at idle, and then fi nally went away leaving a perfect condition carburetor in front of my hangar? This sounds outlandish but I know the 65's and the Bendix carbs are prone to ice. Anyone with similar experiences please tell your story !

[flyguy]

Re: Carb Ice Question

Just my experience, but never had carb ice on any of my three Taylorcrafts. Two 65's and an 85. Because of this I have tried to develope it under perfect conditions staying at altitude over the airport and could never get any. Don't remember any problems with Cessna trainers or my 172, all Continentals.
Used to get it regularly on a Datsun 510 sedan that I had, almost every night, misty/foggy probably low 40's. Cold engine, run about 1/4 mile, pop bang poom then ok.

what were the weather conditiions?
Darryl
Just had one more thought sitting here mulling it over. Maybe a sticking needle valve, or debris under it, or the float assembly hanging up. I had a chevy that did that regular and I could just TAP the carb and it would fix the problem. The sign of that is usually black smoke out the exhaust. Just a thought.

Just read the last on your other thread--so much for carb troubles. That was my last guess, I guess.

[Ron Coleman]

Re: Carb Ice Question

Carb ice is a real problem in Ohio around the lakes. I have had serious icing problems in 2 different T-Crafts, Cessna 140 and Cessna 172. I have had near engine failures in all of the planes and have become an expert with the carb heat knob. Main rule...use it often just to see if you get an rpm increase. If you do use the carb heat more.
Almost always carb icing creeps up on you, your engine quiets down and runs gently slower and quieter untill your hair stands on end when the engine quits or barks hopefully clears itself momentarily. I don't recall a time when the engine quits suddenly from ice. The one situation where that happens is when you have carb heat on before takeoff, melting what ice may be in the carb from idling, and then pulling the heat off during takeoff. The residual water in the carb may suddenly freeze under full throttle and the engine may balk or even quit. That would be cool damp conditions. Foggy or rainy and cool. If you have blocked the carb heat you may be inducing icing. Often if you have serious icing you will see water dripping out of the carb while it is melting after you have shut down.
I would never reduce the effectiveness of the carb heater.

There was a long thread on carb icing that you might check out.

RonC

[Mark Julicher]

Re: Carb Ice Question

The problem sounds like it could be a case of stuck needle or improperly set float drop. I have had the engine failure on takeoff due to improper float drop.

I have had suspected carb ice also. Conditions were 60 degree day, high humidity, level flight with engine at 2150 RPM, altitude 1500 MSL.

[Robert Lees]

Re: Carb Ice Question

In my experience, carb ice very rarely happens at full power. There is so little pressure drop between the atmosphere and the inlet manifold with the butterfly fully open, that the only source of cooling is the vapourising fuel (usually not enough on its own to freeze the water out of the air, and with the huge flow of air, probably not enough to allow any ice to form on the carb/inlet surfaces).

At power settings near idle, however, it's a different story.

[Chet Peek]

Re: Carb Ice Question

Almost certainly a fuel flow problem. Try something simple, like was the shut-off valve accidently pull part way out, or linkage loose.

Chet.

[VictorBravo]

Re: Carb Ice Question

As I posted in another thread, I had the carburetor checked in front of me yesterday. The float level (fuel level) checked out perfectly. The float "drop" I believe was good, if you mean the float travel. The needle travel was also good, approx .040" by visual check. The fuel gushed through the carburetor freely during the inspection when the float was depressed by hand, and shut off promptly when the float was released.

The carburetor was checked by an IA who specialized in this same type of carburetor for years and is by all rights an expert on the Bendix carb.

I truly do not believe it is a carburetor problem.

There was no problem in the fuel hose that I could see visually or with a wire probe.

The gascolator screen was clear, as was the carb inlet screen.

I believe the fuel valve was in the on position, because I had done three touch and go landings within a few minutes of the failure, and since this valve is hard to move it would not have vibrated closed.

PLEASE keep the ideas and experiences coming, I am grasping at straws here. There are no good places to land an airplane within five miles of this airport in any direction, save for Interstate 5 !

[Don]

Re: Carb Ice Question

Bill, carb ice and rubber from the fuel lines have been mentioned, but nothing said about the possibilty of water in the fuel..Also those rubber tipped needles have caused problems in the past?????? I just sent my carb for my 85 in to be overhauled......Good luck,..............Don

[tawadc95]

Re: Carb Ice Question

mag switch? maybe a wire exposed somewhere that touches metal as it vibrates or passing through the firewall?

[jstall]

Re: Carb Ice Question

I am thinking my recent engine failure on takeoff MAY have been caused by carb ice. It is a stretch, but a possibility -

I had flown three touch and go landings, the last one within ten minutes of the engine failure on takeoff. On each touch and go, I used carb heat from downwind abeam all the way to touchdown.

HOWEVER, I had moved the carb heat air scoop form the front cylinder baffle to the oil cooling baffle (in the square hole under the propeller). Since I was running cold oil temps and high cylinder temps, I thought I should start covering the oil cooling opening to raise the oil temps and hopefully cool the cylinder temps (keeping less high pressure air from going into the lower cowl). On the last test flight I had over 80% of this square opening taped off. The result was still 165F oil temps. But there was definitely LESS airflow available to the carburetor heat air scoop because of my taping off the oil cooling hole.

HOWEVER, the airplane ran perfectly and did not suffer any known carb icing on the three previous touch and goes in the same configuration (oil hole 80% taped).

After the third touch and go, I parked the airplane in the runup area for about ten minutes while I made an adjustment to the cowl. So the warmth of the engine soaked through the carburetor for a few minutes. The engine restarted normally, I taxied out to the runway and started takeoff, when the engine RPM suddenly dropped off as though I ran out of fuel.

After I stopped the airplane in the dirt next to the runway, it started up fine, idled for a couple of minutes, and quit while idling.

I pushed it to the tiedown and repeated the startup, and it quit again in a few minutes.

A local T-craft owner and IA mechanic came over while it was running the third time, and unlatched the primer, and it ran rough but did not quit.

I taxied it back to the other side of the airport, and in front of my hangar did a full throttle runup for ten seconds, with no problems whatsoever.

The flexible fuel line was not broken or filled with debris. The gascolator was clean. The fuel in the airplane had no water. I had at least 4 gallons in the tank.

Does this sound like it could possibly be carb ice to anyone? Could I have built up some carb ice in the three touch and goes that stayed in ice form for ten minutes of a warm parked airplane, then caused an engine failure on takeoff, then three more at idle, and then fi nally went away leaving a perfect condition carburetor in front of my hangar? This sounds outlandish but I know the 65's and the Bendix carbs are prone to ice. Anyone with similar experiences please tell your story !

Well, don't know, but what you are describing is what I had happen to me "ONCE" and thankfully only once back in 1984 Georgetown TX, and my Cessna 190 quit me or 70% of it gave up on takeoff, from Georgetown
pulling back power would kinda get it running again, but wouldn't pull enough to fly, I just barely got back on airport, would idle but wouldn't run above that, everything looked hunkey dorey, I sumped it and no water, nothing
all looked good. then after that sumping deal, it ran perfect and never did it again. I was running TEXACO GASOHOL, I'm sure it vapor locked, thats
very far out for the T Craft in Winter, but if you have some Gasohol in there
and the fuel line strainer to carb is close to something hot, It could be. I wouldn't factor that out

JS

[flyguy]

Re: Carb Ice Question

Isn't vapor lock a fuel pump problem??
DC

[jstall]

Re: Carb Ice Question

Yes, vapor lock is a fuel problem, but usually doesn't come on unless something has changed to trigger it, such as lower vapor pressure fuel
such as gasohol, or a change in the routing of a fuel line to get it hot
as it wasn't before, or, extreme OAT'S of which we don't have right now. So I don't know, but it could be, check your fuel, are you using AUTO FUEL?, if not, vapor lock probably isnt an issue, also be sure nothing in the lower cowl is putting undue heat onto or in the viciinity of the carb or fuel lines. otherwise, don't know, but what you decribe is that the carb or engine is starving for fuel, a blocked line, as Buell mentioned, vapor locking
another, even a sticking float

JS

[Guest]

Re: Carb Ice Question

Bill,

I have experienced the same thing on take off about 3 times (that I recall) in ~40 years.

I have never had the fail at idle on the ground afterwards though.

Each time at take off I had low fuel and high nose.

One (the first) time resulted in emergency landing, two times lowering the nose perked it up and on I went.

Dave.

[Len Petterson]

Re: Carb Ice Question

It takes 72 deg F to evaporete gasoline in a carburator, I have been told.
If if you detuct what from your outside temperature and factor in a high humitety you have carb ice.
Yes it sound like carb ice to me. If the engine ran after sitting a while
You can create carb ice by adding carb heat if the heated air is to cold or the natural conditions are right.
I hade a case of carb ice in a C 85 doing tuch and goes, on a nice winterday 5 degF 3 miles from lake Erie. Cold but high relative humitety + carbheat from a not fully warmed up engine after a longer final at 1200 rpm The engine coled of to much!
If you have Etanol in the gas, it should be less chanse of carb ice according to some " experts". I ???????? it.Prove it to me!(;f
Some of you also fly behind or infront of two strokes
They need more heat to evapurate fuel and oil mixtures when the 72 'DegF becuase the oil in the fuel.
Len

[btbell]

Re: Carb Ice Question

About a year or so ago our T had a similar problem on the ground. Started fine and idled fine but when advancing the throttle above 1200 RPM it struggled and wanted to quit. I could put the throttle full forward and only get about 1200 RPM.

Long story short it turned out the be a stuck float. Just a tap on the carb resolved the issue. We since have a new engine and carb on the plane and have not had the issue happen again.

Brian