The Stovebolt Site Forums The Shop Area Engine Shop frost on carburator

I am experiencing this in 40 degree air temp. here in Wisconsin in November. I had frost form just above the insulater on the lower end of the carb. What causes it and should I put my tongue on it?

Thanks - Scott

Carburetor icing between 38 and 40 degree temp in high humidity is common. Air rushing through the carb pulls heat out of the metal. When humid air comes in contact with the metal, it condenses and forms ice, both inside and outside of the carb. Most people don't drive far enough to notice the ice on the inside. Back when these vehicles were all we had, it was common for them to lose power and smoke black like the choke was pulled out after about a half hour of driving. This was caused by the venturi becoming smaller because of the ice. A common fix was to take a leak on the carb to warm it up.

A common fix was to take a leak on the carb to warm it up. [/quote]

...and I sez, that will also help unstick your tongue when it gets frozen to the carburetor.

You might want to try rigging up a warm air feed to your air cleaner from the exhaust manifold area...a little sheet metal shrouding and a piece of hi-temp. hose to draw in some pre-heated air.
DON'T put your tongue on it, or eat any yellow snow.

I had a car that I removed the carb heat riser to that would ice up every fall and spring in Wisconsin. It would get to the point where the car ran like crap. Pulled over, the engine heat would rise, then I could drive for another 30-40 miles. While taking a leak on the carb may have helped, the smell of warm urine coming thru the vents would not be a good thing.

Eventually I quit driving the car in weather colder than 50.

Make sure the heat risor valve is working.

The heat riser really doesn't do anything after the engine is warmed up. It warms the manifold when the engine is cold, but it didn't sense carb icing. Once it opens, it stays open. We used trucks to deliver heating oil. Parking them in 40 degree weather wasn't an option.

When anything, including gasoline, evaporates, it consumes heat. The venturi area of the carburetor, where the fuel vaporizing starts, is acting like a small refrigerator. From there to the the throttle plates, the temperature can drop enough to freeze the moisture in the air, inside and out, particularly when the temperature of the incoming air is close to freezing and the humidity is high. Airplanes have a "carburetor heat" system to draw air past the exhaust before it enters the carb to prevent carburetor icing and possible engine stalling. Modern automobiles have a similar system, where the air is pulled through a sheet metal shroud around the exhaust manifold during warmup, and redirected away from the heat after the inlet air temperature rises. The small accordion-pleated hose that is attached to the intake snorkel is the hot air source during warmup, and there's a flapper valve in the snorkel to swap over to cold air when necessary.
Jerry

carry a spray-can of de-icer with you.use when needed

Thanks for the tips.

Scott

....for what its worth dept. I was reading an OLD CARS WEEKLY paper tonight and reading the question and answer section I read where having an oil filter in front of the carb would make it frost over?????????????????

Did any of you see that? ....I feel sure I read it correctly .......IF scdascda is running an oil filter up in front of it perhaps it could be his problem?? I say IF!!

That makes no sense to me at all. We experienced carb icing with our GMCs that had the filter in front of the distributor and also on my cars with Y blocks that had the filter down low under the exhaust manifold.

I agree Ken, if anything, having an oil filter in front of the carb would give off more heat from the hot oil.

I've experienced carb icing while flying a carbureted Lycoming, scary minuet or so till the carb heat kicked in. I was low and slow a few miles out from the pattern waiting for the traffic to clear when the power just started to drop off. It generally only happens when the engine is throttled back like on landing where the butterfly is only partially open. It's standard operating procedure with any carbureted air-cooled engine to add carb heat as soon as you throttle back on your approach or if you experience a gradual power loss. AOPA has a real good Safety Advisory out on Aircraft Icing. Page 11 & 12 discusses induction system ice. Keep in mind that the engines they are discussing are air cooled engines taking air in directly from the out side, not water cooled engines with the intake inside the engine compartment and behind a radiator as in our ADs. Carburetor icing in and automobile engine is quite rare.

I might add that in my biplane I have a Lycoming IO360 with Bendix fuel injection and no carb heat is necessary.

I don't understand why in a water-cooled stock Stovebolt, if the throttle is open and you’re running along at highway speeds, why your carburetor would ice up. I might be able to see it if you were stuck in heavy traffic and idling for a long period.

A few years ago, using a laboratory digital thermometer I did some temperature studies on my stock 1950, 216. Measurements were taken all around the intake manifold flange and at points all around the Rochester carburetor. I was trying to isolate the percolation problems we have with them at shut down. It's surprising how much heat is transferred up to the carb float bowl by conduction after the engine is shut down. When the engine is running the cast iron base runs cold as would be expected because of evaporative cooling but not enough to form ice.

Denny Graham
Sandwich, IL

Jerry (Hot Rod Lincoln) has an excellent explanation in his post.

Carb icing is very common on older inline 4 and 6 cylinder engines. I have only once personally experienced icing on a V-8, but that was a Holley carb which explains this unusual occurance. Carb icing normally occurs between 25 and 40 degree F. when the relative humidity is quite high (rain, fog, snow, etc.) and generally at highway speeds. If icing is experienced, normally pulling to the side of the road, and running the engine at a fast idle for 30 seconds or so will clear the icing.

The reason for icing at highway speeds is twofold: (1) there is more fuel going through the carburetor, thus more heat (called the heat of vaporization) is required to vaporize the fuel and (2) at the higher speeds, there is more air circulating under the hood removing the engine heat at a greater rate.

Carburetor tune also plays a major factor. A carburetor with an overrich mixture is more prone to ice (which explains why my Holley, notorious for running too rich, iced on a V-8).

For several years we have suggested that owners of older vehicles could acquire an air cleaner from one of the early 1970's Toyotas or Datsuns which had a snorkel with a flip switch to control fresh or heated air. Hook this switch up to a choke cable, and the heat could be controlled from the driver's seat.

Jon.

Holley 3 bolt carbs like Y blocks and 302 GMC used were probably the worst about icing. We always ran a little over rich mixture to get longer life out of our valves. Of course Zenith did it too. It was always in fog or high humidity and 38 to 40 degrees seemed to be the window of icing. However, in Texas, colder than that usually means a blue norther with cold dry air.

Carb icing, I get that about every single day here where I live, this time of year. In fact, that's part of the reason I moved from the single barrel, to the offy and two Carter W-1's. I figured, two carbs, each with half the airflow... Now I have two frozen carbs, about 2 minutes after start up, the truck starts to stumble, and dies. I have the manifold heat on the carbs. I just wait a few minutes, as the exhaust headers warm up the carbs, and away I go!
When I have a little more time in the morning, I just put the trouble light in there, and let it warm up the carbs.

I have never had icing on the highway though.

Here is a picture link, of my old Rochester B, freezing like a bastard.

http://i221.photobucket.com/albums/dd45/HomeCrafter/IMG00014.jpg

Boy Chris, that sure looks odd, why wonder why the nuts in direct contact with the cast base aren't frosting up and yet the phenolic insulator block is?

Denny Graham
Sandwich, IL

Ohh, she was just getting started with the freeze. After another minute, the whole works would be frosty.
The nuts were still warmed by the manifold studs, it was a few degrees above freezing out you see. The carby freezes from the inside - out.

Sounds like what the old Lycoming engines experiance in the airplane world. They typically have a lever in the cockpit to pull for carb icing. Typically re-directing some exhaust manifold heat to the carb area, to clear the obstruction....
Probably came about as it was hard to pee on the carb while in flight...

Sounds like someone didn't read the entire thread!



Stuart

Hahhah Skidmarks is a funny but good nickname

Ok, I realize this thread is about 3 months old, but I'm really interested in how a person might resolve the problem. Yesterday I started my truck and I was working under the hood. After about 10 minutes, I noticed the carb started icing. It looked a lot like the photo in Mr. Lang's post.

The Carbking recommended to get an air cleaner from a Datsun or Toyota which has a snorkel and a flip switch. Can anyone elaborate on that a little with a picture or drawing? Has anyone done this?

Starfire4 recommened running a warm air feed from the exhaust manifold to the air cleaner. Again, I understand the concept, but has anyone done this?

I'm really just looking for ideas.

Thanks for your thoughts.

Here's what I do:
I use my block heater for a few hours in the morning before I start 'er up. This warms not only the engine, but also the manifold and the carbs.
Before I put the heater in, or if I don't have time, I just start it and wait. After about three or five minutes idling to warm the truck up, it starts running really rough. At that point, its iced up. So, I turn it off, wait about three or five minutes, with the hood closed. This let's the manifold, and carbs warm up just enough, that when its started again, away she goes!!

But, I live in the pacific northwest, (drive my truck every day) and here its super humid. We are often pretty dang close to the dew point here in the morning.
I'm sure others have different ways of dealing with it.
In fact, you can also leave the trouble light next to the carb for a while to warm it up.

I can elaborate with a verbal "picture".

The air cleaner has a snorkle with a normal cold air intake; but the bottom of the snorkle tube has a round hole which is attached to a tube the same size as the air intake.

On the side of the snorkle is attached a flip switch which flips a hinged door inside the snorkle. When the switch is in one position, cold air in inducted through the snorkle.

When the switch is in the orther position, air is inducted through the tube. The free end of the tube is attached to a piece of sheet metal which wraps half around the exhaust; thus air throught the tube would be warmed by the exhaust.

Jon.

Thanks Christopher and Jon. I understand now.

I routinely had carburetor iceing in an International V-345 engine with a Holley 2 bbl carburetor, and also with Ford V-8, Autolite-Motorcraft 2 bbl carburetor. Both had manifold heat, but both would ice up in cool, damp weather, but only during the first couple of miles of stop-and-go driving. Without any stops in the first mile or so of driving, the engine heat would warm the carburetor enough to clear the ice and you wouldn't notice anything after that.

The early Corvairs were prone to carburetor iceing at highway speeds, but it took a long time to cause any trouble. Those were/are 6-cyl, air-cooled, flat engines, like the air-cooled airplane engines. The remedy for the Corvairs was to change a heat insulator under the carburetors (both of them). With the V-8s, just about any of them, the main trouble was inoperative heat riser valves and plugged heat passages in the manifold/carburetor base.

The difference between the two iceing situations (V-8 and air-cooled flat six) is where the ice forms- in the V-8s the ice formed at the thorttle valve (throttle ice), which would block the idle and low-speed discharge ports and stall the engine at idle speed. In the Corvairs, the ice formed in the venturi and slightly below, and would eventually throttle the air flow and block the fuel main discharge nozzles- stalled engine, even at highway speeds.

I don't know if the VWs had the same carburetor ice problems as the Corvairs, but I suspect they did.

In the airplane engines, I think the issue is more venturi ice, but that is academic; you don't want the engine stopping anywhere off the ground.

Harvester

The VWs had heat tubes coming from the exhaust manifold. I never noticed any icing with them hooked up. But on our dune buggies with headers the outside of the intake manifold would ice up in hard running even on hot days.

I'm a marine tech, and found this thread intesting. I had an ice problem on a 5.7 TBI injected engine. Ice around the lower part of the throttle body and butterfly valves. Problem with it is that it freezes the nearby MAP sensor, causing the engine to stall out. See... even happens on the newer technology. I found the heat transfer pipe from the exhaust manifold to the intake manifold was kinked, not letting enough heat to keep it all warm and ice free....