Carburater keeps iceing

[mitchell]

My carburator on my 1936 chysler flathead keeps iceing up after running for a hour or so.. Can somebody help me with this ????

[BETTY-B]

It's probably those extreme cold temperatures you people have in the Arctic...

DAN

[pcford]

My carburator on my 1936 chysler flathead keeps iceing up after running for a hour or so.. Can somebody help me with this ????

Do you have a crankcase blow-by tube in place?

[Tylerdurden]

Heat exchanger from the exhaust to the spark arrestor will do.
Add a butterfly valve to turn on/off.

Another way is small Hydronic base board section in place above the carb with a valve to feed cooling water just after it has passed the exhaust.

Any way you can pre heat the air will do. The blow by tube is simplest though, on old motors it could be an issue with fouling though. I like clean air.

[Excalibur]

I'm totally up with PC on this one. Bet you don't have a blow by tube and you need one. Try here for more info:

http://www.jalopyjournal.com/forum/archive/index.php/t-14648.html

[Tom Robb]

I thought all old carb motors had an exhaust manifold passage that blew some exhaust gases into a passageway in the intake manifold that ran under the carb and warmed the thing. My Dodge V8 did.
Ya need carb heat in some conditions. Evaporating/vaporizing gasoline sucks the heat out of the carb and can frost over. Marinized exhaust manifolds don't have this?

[SamSam]

Why would not having a blow-by tube cause the carburator to ice up?

[paladin]

expanding gas and air in a venturi cools things down.....add carb heat or switch to fuel injection....

[nedL]

Interesting problem. I'm not sure what an easy cure would be. I don't really think the blow-by tube (really a crank case breather) will do much at all, especially if the engine is in descent shape. If it is getting really tired then there might be enough blow-by to warm the intake air (but I hope not). Remember this is an updraft carburetor (sort of looks like the bottom third of a saxophone), and the crank case breather on this engine does not enter directly into the carb., it ends a couple of inches in front of the flame arrestor. I never had this problem with my flat head Graymarine, maybe I just haven't run it in cold enough weather. I'd be interested in hearing if you find a solution.

[Lew Barrett]

Chuck's answer is the short sweet one and quite correct. It's all about making a refrigerator when liquid gas is mutated to "vapor" (sort of) in the carb jets. Bear in mind that updraft carbs as used in flatheads sit to the side of the motor, whereas downdrafts as in OHV mills usually/often are atop the lump, and since heat rises.....

Another aspect of carb icing suggests that the ER in question is very wet. In a really dry environment, there would obviously be less moisture in the air. But the bottom line is you need to do something to raise the temperature at the junction where fuel is "squirted" into the motor.

Ned, this problem frequently goes away of it's own accord with regular use. Don't ask me why, but it does.

[kulas44]

Just some heat. Carbed engines in autos had a housing on the exhaust manifold attatched to a duct that had a vacuum valve in the breather snorkle that was contolled by engine heat that closed the flapper to outside air and brought heated air to the carb. Whatever it takes, just get some warm air into the carb, The "latent energy of evaporation" will freeze a carb in a cool and humid environment, but it's really neat to see. A fuel heater would be helpfull, if your engine is a closed type system. A simple heat exchanger, like a gear cooler, inline with the circulator pump, that would warm the fuel would work. they're cheap.

[oldsub86]

http://i131.photobucket.com/albums/p294/oldsub86/Image004.jpgWhere is the exhaust? If it is on the same side of the engine as the intake, you might make a bit of a metal box to put around the carb and hold in heat from the exhaust. That is what snowblower manufacturers do to keep the carb warm. If you look at the photo you will see a black metal box on the side of the engine that covers part of the muffler. The carb is inside that box. It will receive heat from the engine and the muffler.

Randy

[pcford]

Why would not having a blow-by tube cause the carburator to ice up?

Blow-by is hot.

[Excalibur]

Why would not having a blow-by tube cause the carburator to ice up?

Not having a blow by does not cause carb icing. Vaporising fuel in a partial vacuum (the venturi of the carb), on a cool humid day causes icing. Having a blow by tube connected to the flame arrester adds heat to the incoming air and helps prevent the icing.

[Tylerdurden]

Well you have 3 options. Two actually work and one is hit or miss.
Your choice.

[Ron Joslin]

Tow it down to Florida. That will fix it and you won't even need any tools.

[Bob Adams]

The blow by tube will help. I suspect you have a cast iron Zenith updraft carb. They were suceptable to iceing.

[SamSam]

Not having a blow by does not cause carb icing. Vaporising fuel in a partial vacuum (the venturi of the carb), on a cool humid day causes icing. Having a blow by tube connected to the flame arrester adds heat to the incoming air and helps prevent the icing.
OK. I was picturing the old ones that just hung down the side of the engine pointing at the ground. Connected to the air intake would be different.

[PaulC]

It would be interesting to see how well dry gas (aka methanol) would work? I don't know your tank size so I don't know if the volume you need is just a can full (practical) or drum full (not practical). Might be handy to have some aboard if the problem just goes away as the weather gets warmer, and then comes back in a vengeance next fall, when you least expect or are prepared for it. Good luck with it and lots of good advice above

Note: alcohols can be real hard on some types of seal material, just so you know!

[pcford]

OK. I was picturing the old ones that just hung down the side of the engine pointing at the ground. Connected to the air intake would be different.

There are not really connected...there's a quarter inch or so of clearance.

[Bob Adams]

Dry gas may make things worse. I'd think it will lower the boiling point (alchohol evaporates faster than gasoline) making the refigeration effect in the venturi worse. The ice is formed from moisture in the AIR, not the fuel.

[PaulC]

But alcohols bind up with the water and significantly lower the freeze point.

[Tom Robb]

It isn't the fuel that freezes - it's the moisture in the air that freezes as the evaporation/vaporization of the fuel sucks the heat out of the carb.

[Lew Barrett]

If you're going to dry anything, start with the ER. Put a heater and some ventilation in there when not underway.

[SamSam]

Originally Posted by SamSam http://www.woodenboat.com/forum/images/buttons/viewpost.gif (http://www.woodenboat.com/forum/showthread.php?p=1794188#post1794188)
OK. I was picturing the old ones that just hung down the side of the engine pointing at the ground. Connected to the air intake would be different.

There are not really connected...there's a quarter inch or so of clearance.
I'm talking about the tube that's connected to the flame arrester or air cleaner that feeds blow-by into the air intake of the carb. Are you referring to the tube itself or the blow-by being used as a heater for the body of the carb?