Icing

[Gannet]

As it is winter here on the top half of the rotating sphere, I thought that I would ask a seasonal question.

Do Seagull carbs (specifically small choke Villiers) ice up in cool damp conditions? It really seems unlikey to me, but I thought that I would ask.

Years ago when cars had unheated carbs, my journey to work on a cold damp winters morning, often resulted, after about 5 minutes running, in the car getting slower and slower due to the carb icing up. Switching off and coasting for about 10/15 seconds cured the problem; as presumably the ice melted.

Now twice this year when on the river in the early morning when it was about 3 or 5 degC and very damp, my Seagull, after running about 3 or 4 minutes got slower and slower. I stopped it, looked at it, scratched my head and restarted it. It then continued to run at its normal full speed.
Did it ice up?
I realise that 5 deg is not cold, but could the significance be the temperature combined with the high relative humidity?
When I say twice, it was with two different engines. I know fuel starvation and I guess other defects could have caused this, but.......surely it couldn't have been due to icing, could it?
Jeremy

[Keith.P]

I used to have this problem with one of my old stationary engines, as it had twin inlet manifolds that were about 18"+ long, its always been a problem with long manifold engines, like the VW Beetle, but I have never used a seagull in low temperatures before.
The seagull has no manifold to talk of, so I can't see it having much of an issue once the motor has warmed up, unless it very cold.

[Daryl]

I could see fuel containing Ethanol in it causing some problems with icing. Had similar problems with a car with carby & fuel with Ethanol in it.

[Collector Inspector]

Interesting "Icing" at 5 Deg C ambient, never have I experienced such a problem down under as I spent an extra hour or two in bed before venturing out cold mornings using a Gull at my Shack.

Cold for down here at that. It does happen but rare but does happen. I can not comment other than that:

If very cold ambient the negative induction pressure in any carb on any motor, will be tending to lower temps and then concerning RH of the air may well cause a problem maybe.

As I say, I am not experienced in giving a solution here.

Interesting but.

ERrrrr, Etho?..............Maybe give that a big miss anytime Old Dears.

Just a thort aye?

Regards

B

[Gannet]

Bruce,

Yes, I think your thought of staying in bed until it warms up is probably worthy of action or more accurately, inaction!

Perhaps, I should ask Stelios in Greece - somewhere where it is often cold and damp! I am sure that he would make a comment.

Daryl, - Ethanol? Alcohol evaporates very readily causing a drop in temperature due to latent heat.
However, Christmas and New Year festivities will soon be underway when other alcohol based mixtures will be tried with and without ice and hopefully without any evaporation!

I think in future I must play boats and outboards in sensible temperatures, and not think too much about one off (or even two off!) unusual events!

Jeremy

[charlesp]

I haven't any experience of carburettor icing on a Seagull, but I can't think of any occasion when I have used one in very low temperatures.

In the early days Marston literature made much of the fact that the carb was 'pre-heated' which after long discussion the other (older) Charles and I reckoned was simply a reference to the inlet spigot being the same casting as the water jacket. Possibly this is negated by the generous water flow of the Little Model Forty and her sisters?

I have never seen any reference to icing in any of the technical bulletins or news letters, nor heard mention of the phenomenon locally.

I can tell you that Marstons were used by a Greenland expedition in the 30's and Seagulls by an Antarctic expedition in the 60-'s/70's, the reports I heard say nothing of icing nor of precautions taken to prevent it.

I admire your hardiness!

[Gannet]

Charles,
I was interested to read you reference to Antarctic expeditions using Seagulls. A wise choice of outboard.
I suspect (ie guess) that when icing occurs (if indeed it ever occurs), the high humidity of the air is a prerequisite. Maybe cold dry air doesn't have enough water in it to cause a problem. Logically completely dry air cnnot cause a problem. Wouldn't the air in sub zero polar regions be very dry?
I think also that there is a critical shortish timescale of engine running before the 'pre-heated' carb gets sufficiently warm from the engine heat.
I am sure the topic is probably in reality just academic, but nevertheless I thought that I would post my experience. Especially as there is a current post suggesting that this forum is not 'lively'. Although I admit this topic is hardly exciting .....
Jeremy

[charlesp]

Good point about dry arctic air, I hadn't thought of that.

I can't help but wonder just how warm the carb could get - I wouldn't have thought by much, but I've never consciously touched a carb while running.

As further testament to my ignorance I have to ask - which part of a carburettor would be affected by icing?

[Gannet]

I don't really know exactly where the ice would form. Somewhere in the choke/venturi area, I would have thought.
The effect is to reduce the size of the choke/venturi, thus restricting air flow and engine performance.

[lakeviewlad]

I've been out in all weathers and through semi-frozen lake with my 1947 102 and have never experienced icing around inlet. There was ice around my "inlet" as the mist does have a habit of freezing on one's beard...

[robm]

Carb icing occurs due to a drop in temperature as the air flows through the carb venturi . This is a result of the physics of compressible flow.
(I could have learned a whole lot more in that course if the prof had ever mentioned carburettors even once.)

The air flows through the venturi, the temperature drops, the moisture comes out of the air and forms ice inside the carb, blocking flow.

I find it occurs when the temperature is about 2 deg. C or so, and very high humidity. It usually happened to me on the highway, with the primary barrel of a 2 BBL vacuum progressive carb wide open, and the secondary not yet open much if at all. This was a 1971 Datsun PL510, not sure what they called it outside of North America.

It is possible that a Seagull may be used in the conditions where icing can occur. But I suspect the flow through the carb is not fast enough to cause the temperature drop.

Has any one found a bigger carb makes more power on a Seagull? If so, it may be getting to the point where icing may occur in the right conditions.

[Charles uk]

Rob I thought that the temperature drop in carbs was caused by the fuel vaporising ( try dipping your hand in neat petrol & then shake it around, try it with water next, petrol's colder), not such a problem in the carbs that Seagull used, as they are designed to pass the fuel/oil mix into the crankcase in a mist of very small droplets, which when they come into contact with the hotter parts of the engine (components that are subject to frictional loads or the heat of combustion) like the crankshaft, conrod, crankcase around the bearings, piston & upper cylinder walls, which are then cooled by the petrol vaporising leaving deposits of liqued 2-stroke oil, which doesn't vapourise as it requires a much higher temperature.

Whilst it's true that the lowering of pressure caused by the carb venturi might cause a slight lowering of temperature, plus that of some fuel vapourising, this tends to be partially negated by the heat gain from the sudden rise in pressure when the inlet port closes stopping the rapid flow through the carb.

I've never suffered carb icing during my Seagull racing efforts, when I must pass approching 700 litres of fuel air a minute through the carb rather than the 400 ish litres a minute of a standard Seagull at full blast.

[Grumpy]

Absolutely correct except that idea of putting your hand into petrol and then water and shaking it all about is not such a great idea.
Much like putting high octane fuel onto a bbq.
I tried the shaking trick, noticed with petrol it was colder than with water then observed the cigarette between my 1=2 fingers burning brightly and watched the smoke rising lazily upwards then drifting slothfully sidewards with the gentle zephyr of a breeze.
Then, heaven forbid I burst into flames, eventually also taking out 3 houses in the neighbourhood , 8 visiting relatives and leaving myself with damnable slight burning to my right hand.
Will have to either cease my xmas time bbqs ,purchase a country estate or go for KFC or MCDonalds
And nobody is accepting any of my apologies.