Carb Ice Question

[VictorBravo]

Re: Carb Ice Question

Thank you all for the ideas, however the carb checked out FINE, and I was using 100LL airport fuel, which I drained out of the gascolator less than two minutes after the failure and showed no water.

I'm thinking that I possibly had a big chunk of ice develop over the previous three touch and goes, and that this ice melted while the plane was sitting for ten minutes with a warm engine, and then when I went to take off the water/slush was sucked out of the filter airbox and back into the engine.

That still does not fully explain why it would quit when idling. Anyone have any ideas about that?

Bill

[tawadc95]

Re: Carb Ice Question

Bill,
What is your idle speed like? If it is to low it can engage the impulse couplers and that will stall the engine assuming you have coupled mags.
I could see where it would be possible if you were at a higher msl alt airport making a richer mix and 1 coupled mag and carb heat on to create a rich mix to lower enough rpm at idle for an uncoupled mag to keep up or to engage both couplers if you have 2
Did you have the engine at idle on a long final without clearing it out

[VictorBravo]

Re: Carb Ice Question

Bill,
What is your idle speed like? If it is to low it can engage the impulse couplers and that will stall the engine assuming you have coupled mags.
I could see where it would be possible if you were at a higher msl alt airport making a richer mix and 1 coupled mag and carb heat on to create a rich mix to lower enough rpm at idle for an uncoupled mag to keep up or to engage both couplers if you have 2
Did you have the engine at idle on a long final without clearing it out

My idle is about 600-650 unless I tug it hard back, and then it will go to 500 or so and I can hear the impulse couplers clicking occasionally. But I never pull it that far back in the air.

I did have it on a long final without clearing it out, if you mean raising the throttle.

[tawadc95]

Re: Carb Ice Question

that is what I meant
you can load em up and dirty plugs without opening the throttle occassionaly on a long final and they will stumble pretty good if you need throttle for a go around until it cleans out.

[Bojambles]

Re: Carb Ice Question

Take a look at the intake pipes and induction system components after a few minutes of idle in a high humidity environment.

Around here they are usually dripping wet on the outside. I can only imagine what the venturi throat looks like under those conditions, which are common around here.

I have had carb ice several times on take-off with my A-65 after extended periods at idle (long taxi and/or long wait for take-off).

My cure is after mag & carb heat check, I use full carb heat until time for take-off, then full forward with the throttle followed by full forward with carb heat.

Have not had a problem in 25+ years using this policy.

Have also had carb ice a cruise, was a very un-nerving to pull the carb heat and loose yet more power, but after what seemed like an eternity (probably only 10 - 20 seconds) it cleared right up, and resumed full power.

[Gary Snell]

Re: Carb Ice Question

On my second flight after my rebuild, engine quit on climbout (came back when nose was lowered). Nose was high and had about 4 gals. in the tank.

Prior to next flight:
1- Replaced metal line from tank to bowl. There was an ever so slight kink that may have restricted some flow.

2- Disassembled the Stromberg. Float needle/seat opening was not per spec for a gravity feed system with low head pressure. Noted it was OK for pumped system. Changed out the seat.

Worked fine ever since (50Hours).

I would still be suspect of leaning being the culprit given the high CHTs. If you had worn throttle shaft bushings, may be varying degrees of leakage depending on throttle position. Leak might be exacerbated when holding pressure on the throttle shaft during full throttle??

[Guest]

Re: Carb Ice Question

On my second flight after my rebuild, engine quit on climbout (came back when nose was lowered). Nose was high and had about 4 gals. in the tank.

Prior to next flight:
1- Replaced metal line from tank to bowl. There was an ever so slight kink that may have restricted some flow.

2- Disassembled the Stromberg. Float needle/seat opening was not per spec for a gravity feed system with low head pressure. Noted it was OK for pumped system. Changed out the seat.

Worked fine ever since (50Hours).

I would still be suspect of leaning being the culprit given the high CHTs. If you had worn throttle shaft bushings, may be varying degrees of leakage depending on throttle position. Leak might be exacerbated when holding pressure on the throttle shaft during full throttle??

Hey Gary,

Your post really got me thinking.

I am aware of the various Stromberg settings an their dependency on the engine and fuel system installation that are in the manual and I use them.

Two of the three times this happened to me was before I overhauled the engine and accessories, including the carb on N43972. The other time was in a different plane.

I have not had a problem in N43972 since that time. When I overhauled the carb I never checked the original carb settings I merely made them right for the application it was going to be in.

Now I wish I had checked may have found what you found.

Thanks, Dave.

[Gary Snell]

Re: Carb Ice Question

Dave

I think it is often overlooked. These carbs get swapped around and the obvious things to check are the venturi and jets for the different HP's. I suspect the float needle/seat being out of spec seldom causes a problem, but if it does it will be when you want maximum fuel flow and the head pressure is at its lowest, i.e. steep climb with minimal fuel in the tank.

[Paul Hester]

Re: Carb Ice Question

My dad had the same sort of loss of power on take off once.

Normal checklist and all pre-flight done. First flight with the spring time weather.

Lifted off the runway just high enough for the landing gear to clear the cattle fence at the end of the field, and one pop and no power.

He set it down safe on the other side of the fence.

As it turns out the shutdown was the result of a bug egg just big enough to get stuck in the hole in the fuel metering disk. The only way to see it was to hold the disk up in the light and you could see dim light through the bug egg.

Dad tossed the metering wheel and flew the nex several years with no problems without it.

[crispy critter]

Re: Carb Ice Question

What is a metering wheel...this is a new one on me?

[Guest]

Re: Carb Ice Question

What is a metering wheel...this is a new one on me?

maybe the little disc with the holes in it that mixture control turns??

[flyguy]

Re: Carb Ice Question

I've found a lot of crap in my gas tanks and carbs over the years, but no bug eggs so far. Just lucky I guess. Next time my engine sputters no doubt the first thing I will think is, "Oh S**t, a bug egg. lmao. Funny story.
DC

[Forrest Barber]

Re: Carb Ice Question

they usually show up in the idle by pass jet in the Stromberg makes for rough idle, would not effect the high speed side.

[Paul Hester]

Re: Carb Ice Question

correct it is the little disk with with different size holes for metering the fuel that the mixture control turns.

[VictorBravo]

Re: Carb Ice Question

Paul Wrote: "My dad had the same sort of loss of power on take off once.
Normal checklist and all pre-flight done. First flight with the spring time weather...."

This might be a possibility, except that the airplane had been flying just fine not ten minutes before this failure.

This might be burying my head in the sand, but the only feasible thing that I can come up with is a strange case of carb ice for one specific reason. I had moved the carb heat air scoop from the standard location (front right baffle) to the oil cooling baffle (in the square opening under the crankshaft). I did this trying to maximize the cylinder cooling air.

I had been running LOW oil temps (because the new oil baffle worked so well), so I started closing off the oil cooling opening. I failed to realize that this was also possibly reducing the airflow into the carb heat airscoop which had been repositioned into this baffle.

On the takeoff where I had the failure, the large square oil cooling opening had been closed off leaving only about 15% of the area open. This was still a larger area than the carb heat airscoop, however the scoop for carb heat air was not directly behind the opening in the cowl. So there is a possibility of a swirl, eddy, stall, diverted flow, etc. etc. that could have starved the carb heat airscoop of air. This would have set the stage for a buildup of carb ice that finally got bad enough to kill the engine, or melt the ice and have the engine swallow the water. There are mitigating factors that go against this theory, but to be honest I've looked at just about everything else possible and ruled it out.

Last night I put the carb heat air scoop back in it's original position. Someone loaned me a digital thermometer with a remote probe, so I can stick ito n the carb and at least get a rough idea of how hot or cold it runs. I'm not taking the carburetor apart and installing a true carb air temp probe.

Thanks to everyone AGAIN for applying their brains to this problem.