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Condensate on carb


Rogillio
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'27 DB Coupe. Noticed a lot of condensate forming on the carb. I read somewhere that this indicates something....but can't remember what it means or where I read it.

Another video. I fixed the leaks in the vacuum tank.....but had to pull start it to get it started. Ran good and started with the starter after it warmed up and furl system was primed.

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It just means that the carb is working correctly, drawing a good vacuum inside and thus cooling the metal, and depending on humidity and outside temperature you can have condensation or even frost. My friend with the Stoddard Dayton, hemi combustion chambers, the carb gets ice cold to the touch......

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The carburetor contains a venturi at the throttle. Below the venturi the mixture expands as the manifold opens out. To expand, the mixture must absorb heat from the surrounds. The area cools, including the carb. You will see condensate on the carb and if it is cool enough (say about 5 deg. C or so) it will freeze, inside as well as on the outside of the carb. If it ices up, the engine will starve of fuel. Just let it idle for a while to warm up the manifolds a bit, shut off for five minutes and restart and you will be OK. The break will let everything warm up from the engine heat. Later cars had a "heat riser valve" in the bottom of the exhaust manifold to direct hot exhaust gas to the base of the inlet manifold to prevent icing. Higher humidity makes it worse.

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Guest DodgeKCL

It's a fact of life with internal combustion engines that use carburetors. It can get so bad that the narrow part of the venturi can ice almost shut with rime ice (frost),killing the engine. When setting up your approach for landing in an aircraft with a piston engine using a carb, you pull out a control on the dash that says "Carb Heat". This deflects some of the outside manifold heat,not exhaust, back into the air intake to keep the throat warm enough to keep ice from forming. It's not a good thing to have your engine quit on final or even before. It uses a "stove' wrapped around the exhaust manifold like those old time car cabin heaters. Also before practicing "stalls" and spins, you pull out the carb heat so you still have power when the maneuver is over in case icing takes over at "flight idle',basically the throttle back to it's lowest setting. It's always a trick to remember to shove in the carb heat afterwards because the added heat can cause detonation or pre-ignition and is not a good thing. It can punch holes in the pistons at high power settings. As Paul Harvey used to say "Now you know the rest of the story".

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Does the '27 have a cold air shutter? I know all the other fours have them. If you read the Book of Information it says it should be adjusted to avoid condensation or icing. I've seen the result of carb icing on a car. When the driver wanted to slow down the car kept going because the throttle plate was frozen in the open position.

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The cold air shutter is located on the heat exchange casting to which the air filter is attached. This is a separate casting bolted to the exhaust manifold. Check that the heat transfer pipe is still in situ. These engines take warm air from the exhaust manifold on the right, via a "Y" shaped steel tube, and connects to a short straight tube (which passes through a passage way between cylinders 2 and 3) to the carb on the left. Often, the heat transfer pipe does not join up with the carb air intake - or is missing altogether! .

Edited by R.White (see edit history)
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I will look. I do know there is a tube that mates up with a tub from the carb (at least I think it makes up) but didn't realize it goes to the other side of the block. The air cleaner is on my to-do list to disassemble/clean and understand. I did see there is an adjustment on the starboard side of the egine on the exhaust manifold that looks like it adjusts airflow....presumably to the carb?

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With '27 having the carb on the right side of the engine I don't remember if it has the shutter. That's why I asked. It's been a while since I worked on one . If it does there is a ring within a ring, both are slotted, might be frozen in one place. The outer ring turns to adjust the size of the opening allowing either all hot air or cold air or anything in between. Do not listen to the BS that frost is good. If the throttle plate freezes in one place while driving you run into things because you can't stop.

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As already mentioned by several, the moisture comes from the air.

If this occurs at all temperatures and conditions, it MAY indicate:

(1) A carburetor is is running much too rich.

(2) A carburetor which is too small for the application.

Much more common on inline engines where the carb has less heat, than on V-8's. If the car is correct for the engine, and in a proper state of tune, will GENERALLY occur when ambient temperature is between 25 and 50 degrees F. and the humidity is high.

Jon

Edited by carbking (see edit history)
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Just to confirm the situation. As you know, the carb is on the left and the cold/hot air regulator is under the air filter on the right. The shutter will hopefully slide shut and the warm air should prevent the carb from producing condensation and icing up. I concur with nearchocolatetown that a frozen carb is dangerous. Dodge Brothers went to considerable lengths to ensure this need not happen.

Ray.

Edited by R.White (see edit history)
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Guest DodgeKCL

Actually carb icing does not happen in Winter. It happens mostly in Summer where the humidity is high and the temp, as mentioned by carbking, is between a set of values. The Great Lakes area of North America suffers from this situation throughout the Spring,Summer and Fall. This is why the fellow is experiencing it now and since he does not use his pride and joy during the Winter and would not see it disappear. For those not living in the Temperate Zone of North America, the winter air is dry and devoid of moisture if the ambient temperature remains below 0C/32F. Kind of an oxymoron with all that snow eh? Your lips crack like crazy as the moisture dries on them while sking. We use lip baum to keep ahead of it and skin cream on our faces. Ice and snow left on a unheated cement garage floor does not actually melt away. It dries up over several days without going through the melting stage. It's called sublimation. Antarctica is the largest desert in the world not the Sahara or the Gobi. No preciptation has fallen in the Antarctic for millions of years. So although Arizona could see the temperature range, for instance,it would not see carb icing because of the lack of moisture. But as I mentioned before you do not want to keep the heat on all the time because it lowers the ignition point of the air/fuel mixture to the point of the engine dieseling. This happened as we will all remember in the 60s and 70s as Detroit tried to control the pollution of our cars and trucks by using air pumps and such. The engines got so hot that removing the spark had no effect. The engine just kept running. You had to drop the car into 'drive' or pop the clutch in gear to stop the damn thing. I can remember walking to my house while the '68 Chev coughed and farted until finally with a big bang it stopped. It was a way of life back then seemly forgotten today. So heating the incoming air too much is not a good thing. Be careful out there.

Edited by DodgeKCL (see edit history)
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