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Carb ice

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wallacedw

Member
When flying carb equipped airplanes you have to be careful of carb ice. So there is a manifold that can direct heat to the carburator. When not in a carb ice condition the manifold is off to allow the engine to attain peak power.

Anyway, I am having troubles with my MasseyHarris 44. It is running very rough almost as if it has a miss. I have done a complete tune up and achieved a bit btter performance from the jerking, stuttering, and stalling I was experienceing.

My carburator gets very cold and even gets a slight frost on it. Could this icing be contributing to the problem? I have got it narrowed to a fuel, air, or governor problem.
Anyone ever had symptoms caused by icing?
 
I doubt that ice is the problem with your tractor. External frost is not at all unusual nor does it directly cause problems. Internal frost does cause problems but it rarely occurs. I suspect a lean fuel mixture. Either the fixed high speed jet needs cleaning or the adjustable high speed mixture needs to be enriched. I do not know which type is on your carburetor.
 
Ok, thanks... frost is a better explanation of what I am seeing. My farmer friend suggested opening the load screw out as it is getting colder. I think that is going to accomplish the same thing. That carb ice idea was a long shot but worth the question. I will update this as I continue...
 
We used to farm with a Ford 901 gas that had an icing issue when it was cold. It would run a little rough for a while, then it would smooth out when the manifold warmed up. Sometimes, the outside of the carb would be covered with ice after it started up.
 
I was taught years ago never tune up an engine until you have done a compression check. You could be wasting your time if the compression is low or have a burnt valve. Also if the mechanical advance in the distributor is not working that will cause it to miss and die under acceleration. The frost on the outside of the carb is common due to the fact that is where atmospheric pressure turns into a vacum thus sucking in the fuel thru the jets. Don't worry about the frost!
 
I've been through the carb ice problem a number of times with a number of motor vehicles. You might try applying heat to the carb while it's trying to run. I'd try a hair dryer. That would/should prove whether it's carb ice or not. If it is carb ice, the easiest way to avoid it is with high quality premium fuel. Mobil Super comes to mind. It will have sufficient anti-icing additives to keep your carb from feezing up. Lots of carbs get ice in them from the faster flowing and lower pressure air in the venturi section. "Expansion is a cooling process". I usually experienced it with big Ford V8s. When temps were in the low 40s and plenty of moisture in the air. Mobil Super prevented it. The only other thing is to direct hot air at the carb or build some kind of a carb shield to capture engine heat and retain it around the carb.
 
Bill, that is what i am thinking. That vacuum/pressure difference is dropping the temps/ I am going to try a heater on it to see if there is an improvement.
I will do a compression test too. Hadn't thought of that.
I played with the load needle under the carb bowl and there was a little change but the stuttering and barking is still there. I guess that is missing.. Kinda like an old fighter plane before it kicks all cylinders in..
I checked the spark from the coil and it is very strong and blue. It was jumping almost a half inch. I haven't done anything with the condenser/points. I don't know what to ask for.
 
Dump a bottle of gasline antifreeze in the tank , and forget about it. Problem solved. The gasline antifreeze must contain isopropyl , not methanol. Methanol will not work. As a matter of fact , dump a can in while the engine is running rough , choking out , and puffing black soot. Within seconds , it will start to run like it should. I'm suprised so many people don't know this. I keep isopropyl mixed with my gas all winter. Never any problems.
 
I put a bottle of heat in 5 gal fresh gas after I emptied the entire tank, cleaned the sediment bowl (all of it - I removed it fromt he bottom of the tank so no residue issue.) Fuel flow TO the carb is fine. nChecked the float, good.. so flow seems to be ok. Mixture I THINK is marginal/ok.. so maybe I need ot think ccondeser/points again? I get fire at each plug. Wondering about timing now.
 
years ago ,my neighbor had a wd allis , every winter he pulled a wool sock over the breather , and he said that stopped the carb icing ,, it worked for him
 
A number of factors cause carb icing on airplanes. At high altitude the air is thinner and enriches the mixture. Pilots naturally use the mixture control to lean it out to save fuel when flying. In icing conditions at altitude there is a lot of moisture in the air which is cold and which freezes when it hits the plane. Also there is cold air blowing over the engine at the speed of the plane cooling the engine. Since the tractor doesn't have cold air blowing over it at 100+ mph, some of the natural heat from the block kinda keeps the carb at least luke warm.

Finally, pilots when landing use the carb heat and full rich mixture as a safety precaution since their life may depend upon it if the engine quits.

Richen the mixture and check to see if you have a fuel flow problem from the tank cause of rust, etc. Put a piece of tin or cover or something to cover the exhaust manifold that extends down over the carb to help trap some heat in there. Nothing too elaborate.
 
Wool socks are WARM. But they also are thick enough that they probably cut some of the air flow and richened the mixture.
 
Carburetor ice is a potential problem with any carbureted engine that doesn't have a source of heat. Most older tractors rely on heat from the exhaust manifold to prevent icing. That's why the exhaust and intake manifold is one piece: to allow heat from the exhaust to keep the carb warm. (I'm not familiar with the MH 44, but I assume that's how it is set up.) Since the outside of your carburetor is frosting, it's fair to say that conditions inside the carb are conducive to icing.

If you are experiencing carburetor ice, then the engine should run just fine on startup, then run progressively worse as the ice builds up. This takes several minutes.

Contrary to popular opinion, fuel additives such as alcohol will do little to prevent carb ice. The ice is forming from water in the air, not in the fuel. And it often forms at the entrance to the venturi and (at low speed) around the throttle plate. The main and idle jets deliver fuel downstream of these two respective locations.
 
You will have to either duct warm air to the carb inlet. Or maintain enough heat on the carb"s body to keep melting the ice.
On airplanes when they talk about manifold heat. They are flipping a damper door and ducting intake air over the outside of the exhaust manifold. Before it"s drawn into the carb inlet.
Hot intake air into an engine increases the tendency for detonation and therefore engine failure. The over rich mixture used on takeoff and initial climb reduces the tendency for detonation.
Adding alcohol to the fuel makes the icing problem worse. The alcohol valorizes at a lower temp than gasoline.
 
we opreate about 17 diffrent massey-harris tractors on our farm and ive seen 1/2 inch of ice on our massey 44 carberator in the winter and one thing i would do is rebuild the carb. the kit is around 30.00 and drain and clean the setlment bowl that should help even with the bowl ive seen water get into the carb and it will cause poor preformance at any speed our 44 has m&w doamed pistons and was dinoed at 63.7hp.but that is with the m&w kit witch is no longer avalable my dad overhauled it in june of 1970 and i came along two months later.but its still our workhorse on the farm so give that a try and see if it helps ill ask my dad and see what else he might think could be wrong.
 
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