The Stovebolt Site Forums The Shop Area Engine Shop Carter YF Carb

I recently rebuilt and installed a Carter YF carb in my truck. It runs great and has a nice idle. But I noticed that after it’s been driven for awhile the throttle body has condensation on it and is damp. The gasket between the throttle body and insulator block is damp too but not enough to drip onto the manifold.

I don't smell gas. It's just damp. I’m wondering if I have the float set incorrectly and/or the mixture screw and percolating is occurring. Has this happened to anyone else out there or is it normal?

There is a temperature drop because of the physical design of a carburetor. If the
temperature drops below the dew point moisture will condensate on the base.
This short article explains it better than a lengthy discussion here:
http://www.flightlearnings.com/2010/03/02/carburetor-icing/

DG

Interesting..... It doesn't happen all of the time. I live on the west coast and it has been humid with temps around 60F to 70F so it does make sense. Thanks Denny.

Mine dose this as well. Some times it is 95 degrees out and if im quick to park and open the hood I can see ice on it. But it in no way has affected my truck yet. Dose it a lot more when its humid. I think it is cool.

That article was written for aircraft engine so the "carburetor icing that they are talking
about isn't a problem we would encounter with our trucks.
Yes, you will see condensation and maybe on the rare occasion frost on the base but
you’re not going to have a problem with the venturi icing up.
The critical point with an aircraft engine is when you are at low throttle setting usually on
a decent. Standard practice on approach with a carbureted engine is to add carburetor heat
but at full throttle where you need all your power or during cruse icing is not a problem.
Air pressure and temperature are closely related and that‘s what is going on thru the
venturi, pressure drops at the wall of the venturi and the temperature drops proportionally.
Now if you’ve coming down out of the mountains at Donner pass on a cool humid
day, and ya got your foot off the throttle, praying that your Stovebolt engine will help out
those smoking Huck brakes, well you just might conjure up a bit of internal carburetor ice
by the time ya get to the bottom.
Denny Graham
Sandwich, IL

I used to drive a 75 dodge van and it would ice up so bad it wouldn't run very good. You had to pull over and let it sit and melt before it would start and run anymore.

My carb ices up here in the PNW. I get frost, and infact, the truck will quit outright. Lots and lots of moisture in the air out here, and ice in the carb to boot.

Here's a pic of my frozen rochester. This happens almost everyday in the winter, unless I plug the truck in, as the block heater, warms the intake and carb up. I'm about 120 feet above sea level in my driveway. The carb will freeze up after about 5 minutes of running when everything is cold.

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

Right about now, the truck quits, then you sit there and listen to the radio for about 5 minutes, and fire it up. The manifold warms up the carb.

My model T would freeze up like this, until I installed the factory hot air pipe. Old Henry knew what time it was.

Carb icing is a problem on the models with an engine speed gov. The space between the carb & manifold doesn't let enough heat get to the carb.

So there you go Mark, some first hand examples. I've personally never had one ice
up inside the throat but if the circumstances are just right it obviously does happen down
here on terra firma.
DG

Carb icing can be a problem under certain weather conditions (generally 25~35 degrees F. and 100 percent humidity).

Carb icing can also be a signal that the carb is running too rich! The more fuel that is converted from the liquid to the gasous state, the more heat required for the conversion.

A very ugly but very effective tool against carb icing is a sheet metal stove on the exhaust with piping of the air to the air intake of the carburetor.

Often, rebuilding the carb will minimize icing; but carb heat is the real answer.

We have experienced LOTS of icing on inline engines (Chevy and Ford sixes, and non-USA fours). The only icing I have ever personally experienced on a Vee engine was a Holley (too rich). The only solution I found was replace with a Carter.

I had one four ice so badly going down the highway that the throttle actually froze in the cruise position. Fortunately, manual trans. When the engine started to die, I tried to pump the throttle and could not; then pushed in the clutch and coasted to the side of the highway. About 2 minutes of very rough running, and the engine heat thawed everything so I could run again. Readjusted the heat stove the next day!

Jon.

I've tinkered with the mixture a bit and that seemed to help. We've had some cold mornings here in southern California but nothing like the rest of the country.

Hey Jon, while we're all tuned into the subject maybe you can give me your thoughts on
this. And or I’d like to hear from anyone else that cares to comment on it.

I've heard it mentioned many times before, that the latent heat of evaporation is a
contributing factor in the temperature drop within the venturi.

My thoughts are that the fuel is only “atomized” in the carburetor, not “vaporized“
therefore since there is no change in the state of the fuel, just the shape, there is no
temperature drop.

The atomized fuel droplets aren't vaporized until they hit the hot surface of the intake
manifold and that’s when the latent heat of evaporation occurs due to a change in state
from liquid to vapor.

So if that’s the case then the atomization of the fuel does not contribute to the
temperature drop in the venturi and the sole cause for the drop in temperature is the drop
in air density.

I’m not looking to argue this view, I’d just like to hear some of your opinions and maybe
stimulate some discussion please.
Denny Graham
Sandwich, IL

Denny, ideally, the liquid would be changed to vapor inside the carburetor. Liquid flowing inside the intake manifold tends to (centrifigal force) be thrown against the outside walls of the manifold, and causes driveability issues.

Adding heat to the intake air aids in the vaporization process.

Jon.

I guess I'm basing my ideas on articles like this, which is excerpted from an engineering
journal discussing the advantage of modern fuel injection over the old carburetors. Point
they are making is that fuel injectors atomize the fuel into a much smaller mist of droplets
than the carburetors did.
"Petrol naturally exists at room temperature as a liquid. Surprisingly, the liquid form does
not in fact burn in an engine. The fuel must first be vaporized before it can be burnt;
liquid petrol burns very slowly, while an extremely rapid combustion is required in an
engine. It is therefore very important to introduce the fuel to the intake manifold as a fine
"mist" which can rapidly vaporize."

Denny Graham
Sandwich, IL

Petrol has a high vapour pressure at room temperature, it exists as a liquid, but readily evaporates.

I'm sure fuel injection systems atomize the gas into smaller droplets than does a carb, but as the atomized fuel vaporizes, it surely draws heat from its surroundings. Even getting you hands wet with gasoline makes them feel cooler, as the gas evaporates from your hand, it takes heat with it.

Denny - this might make a good "different" topic.

But since you asked, I fear your comment may have been taken out of context.

Throttle body injection offers little or no benefit over a carburetor other than to "inject" (pun intended) a degree of difficulty above the average enthusiast's level of expertise; and a cost definately above the average enthusiast's budget.

Port injection will perform better than carburetors tuned by the average enthusiast, as the average enthusiast either does not understand "pulsing" or if he/she does understand, does not have the necessary equipment to tune for pulsing. Port injection is not effected overly by pulsing, as only air is flowing into the manifold runners.

I am not convinced that even port injection will significantly improve power/economy over a properly tuned carburetor. However, there is NO question that computer controlled port injection can significantly reduce emissions.

Jon

Many thanks. You guys have some excellent comments.