The Stovebolt Site Forums The Shop Area Engine Shop carb icing-up

Okay, now that I have the carb back on, not leaking and acc pump working, now my new problem is the carb is developing frost on the lower part of it..I have only run it at idle and am not yet road worthy.
It does NOT have one of those insulator things between the carb and the manifold, but even so, if I did try to put one on, I'd have problems with the linkage.
I don't have a spring on the heat riser flap but it is open right now and since I live in Lower Alabama (LA) I really don't think I need the manifold heat...The truck seems to run fine, just concerned about the icing on the carb...

After the engine warms up, do you still have the icing?

It was designed to have the insulator between the carb and manifold, and same with the spring. The vendors have both items and they don't cost much.

Icing can be caused by a carburetor which is too rich. Since you have only run at idle, how far out (turns) is the idle mixture control screw?

Jon.

I have not had the truck on the road yet, so I don't think I have reached full operating temps yet

There was no insulator under the carb and I don't think my linkage will work if I do install a 5/8 one

The mixture screw is out 1½ turns from seat right now

Terry, when you copy/paste here from another app or elsewhere on the net, you need to change the dropdown to "Using HTML and UBBCode

Bill

Terry: I had the same problem with an inline Jeep. But only in the winter. Not enough heat to keep the fuel "atomized". It wold then get pulled into the intake and drop the temp to freezing. Only happened when the temp and humidity was just right. Put the insulator on and re-install the spring on the EX manifold. If the linkage is too short you can make it longer pretty easy. Just cut it and add a threaded bit in line. Tap the cut ends and lock with nuts.

TerryTucker,

What carburetor are you using?

I now have a Holley two barrel AA-1 carb on my 261 that frosts and then condenses water, until the engine heats up. I am lucky that the engine runs fine even at start-up. There is no insulator under the carb and the original intake is heated with heat tubes from the Fenton headers.

I agree with carbking as to my situation - too much carb (or, at least too rich a carb). I have adjustable jets, so I am playing with the settings.

I have run 700 miles with the carb this summer. The Suburban runs smooth as silk, with plenty of power (15 MPG at 60-65mph).

I am using a 1 barrel carter a yf2100 (I think) maybe I just need to run it more, let it warm-up and see how it acts...It seems to run okay now. I just had a concern with the frost on the carb...It's been in the 90's here

why would you have problems using the linkage as it was designed to be installed? (with the insulator plate) that is what would concern me.

Is the "linkage" you are referring-to a one barrel Rochester B carburetor?

TerryTucker, is your Carter carburetor shown here?

Don't know the answer to that. There was NO insulator on the engine when I got it. The linkage is fairly tight as it is now and adding a 5/8 space would make it even worse. I'm not sure of the purpose of the insulator. If it will help with the icing, I'll try to find one and fabricate some kind of linkage for it

more than likely YES...It is probable linkage for a Rochester...really don't know the difference. All I know is that it is a carter yf 2100s on it now

A isolator will not keep it from icing up at the venture when the engine is just started and idled, it should make it worse. High alcohol percentage, high humidity in the air, over rich settings, all can cause problems. You need some drive time and some tuning before getting to worried about it. Try leaning out the mixture screw.

Joe

The job of the insulator is to keep heat away from the carburetor. The shape of the venturi inside the carburetor causes the air going into the carburetor to drop 30-40 degrees in temperature. This cooling effect can cause condensation on the outside of the carb if the humidity is high. If you have moisture in your gas tank ice can form inside the carburetor. I've had carbs ice up when it was 60-70 degrees outside. If I poured a can of dry gas into the gas tank the icing venturi problem was solved.

Terry, listen to the guys when they tell you about the insulator
and heat riser. The engine was designed to run with both of
them maintaining the proper heat for maximum fuel vaporization,
has nothing to do with the part of the country that you live
in. The engine operates around 180° which is twice as hot as
the ambient temperature in most parts of the country. Because
of the vapor pressure of automotive fuel, the insulator was
there to keep the carburetor from getting to hot and boiling
the fuel
Your icing at the base of the carb is typical of carbureted
engines, and is due to the phase change of the fuel thru the
venture because of the drop in pressure. Same idea why they
designed the human body to perspire when it gets hot, phase
change of the sweat drops the temperature of the skin.
The proper Carter model 2100 for a Stovebolt should be a direct
exchange for the original Rochester 'B' and all the linkage,
i.e., throttle, choke, should fit. If it doesn't, then put an
add in the parts wanted forum and get the correct throttle rod.

Here are a couple of articles for you that should better explain
the process.
https://en.wikipedia.org/wiki/Latent_heat
http://www.hemmings.com/hcc/stories/2009/05/01/hmn_tips1.html

Denny Graham
Sandwich, IL

Okay guys, I am mistaken. I DO have the insulator on the manifold below the carb, it is painted like the manifold so I didn't realize it, but I don't have the heat riser spring. I don't think I should need that here in south Alabama. It seldom gets colder than in the high 40's-50 in the winter time.

I would not worry about a heat riser in that climate.
You say in your first post that it runs fine.
If it ain't broke than don't fit it.

If the humidity is high and you are running it with the hood up, the carb body is a lot cooler than the dew point. Close the hood and drive for 5 minutes and the carb body will be warm. The problem gone.

While you won't notice any lack of performance in warm climates without a properly functioning heat riser, you will experience gas contamination in your crankcase. When the atomized fuel hits a cooler-than-operating-temperature intake manifold, some of it pools up as a liquid and does not burn and ends up leaking past the rings and ends up in the crankcase, contaminating the oil causing inadequate lubrication. Unless your climate is at or around 180 degrees, this will occur until the engine reaches operating temperature without the heat riser functioning properly.

Thumbs up to that Carl, glad some one understands why
they put a heat riser on all the Stovebolts, not just
the ones that were sold in the north.

Denny Graham
Sandwich, IL

The heat riser only job is to warn up the carb faster then the engine can warm it up. Once the exhaust manifold gets hot and the spring relaxes, the flapper valve diverts heat away from the carb and out the pipe. The manifold will be just as hot with a non working heat riser as a manifold with a working heat riser. The only difference will be the amount of time it takes to heat the carb.

A cold start icing problem will benefit from a working heat riser, but again, once the engine is hot, it will make no difference. A warm air pipe to the air filter will also help with icing issues.

Be sure the manifold has the flapper/diverter valve or you can get a serious vapor lock problem from a over heated carb. GM new they had a heating issue, thats why the isolator was added.

Ideally you want a cold carb with a hot intake. The cold carb keeps the fuel dense and the denser it is, the more power it makes. The hot intake manifold keeps the fuel vaporized and as you know, fuel only burns in a vaporized state.

Joe

Joe,
"The heat riser only job is to warn up the carb faster then the engine can warm it up. Once the exhaust manifold gets hot and the spring relaxes, the flapper valve diverts heat away from the carb and out the pipe. The manifold will be just as hot with a non working heat riser as a manifold with a working heat riser. The only difference will be the amount of time it takes to heat the carb."
Given your statement above, specifically "warm up the carb", how can that occur with the insulator in place? My view of how it works is the diversion of heat from the heat riser is to quickly warm up the the intake manifold. The area of the intake manifold that needs heat the most to prevent loss of atomization is directly above heat riser valve, as this is where the flow of atomized fuel strikes before it moves 90 degrees left and right through the runners toward the intake valves. The rest of your post is spot on.

Very true Carl, it doesn't really warm the carb. The heat does circulate around the center section of the intake through casting ports helping heat the cold fuel interring the intake. This is as much "carb heating" as it does, and that amounts to radiant heat only coming off the intake.

Good catch on that. My mind works a lot faster then my typing skill can keep up with!

Joe

Been idleing my 216 quite a bit lately and I noticed last night that there was a very small amount of liquid collected at the base of the carb near the spacer but on the carb. It was in the area of being below where the fuel line connects so I assumed a fuel leak. It wasn't. It was water i.e. condensation.
I wiped it away and it didn't collect anymore as I continued to run & tune the engine.
I have the carb spacer and working manifold heat (brand new spring with 1/2 a turn of tension and free moveable flapper).

I think in my case it's a combination of high humidity area, cold fuel entering a cold carb & engine and possibly an over rich carb condition as I was useing the vaccum gauge method of adj the carb & timing and I ended up leaning the fuel/air mixture some. Pretty much all of the above mentioned causes.
In any case good thread as I would still be scratching my head wondering where the water droplets came from
Dave

When I was trying to get my dual W-1 setup running awhile back, the front carb was sweating a bunch while the rear one did nothing. I found I had installed a bushing wrong in the throttle bore letting air leak past, this in turn keep the carb from sucking fuel. It was easy see which carb was working just from the water and ice on the outside, it was harder to find the problem I created!