Carburetor Icing

[StevenGray]

Was out in my Bradford yesterday and suffered carburetor icing to the extent that the engine actually stopped, air temperature was around 2deg C, it happened after a long (1mile) climb in second gear through a fog bank down the other side of the hill basically foot on brake not throttle, stopped at an island then accelerated in typical Bradford style (slowly) and the engine simply died, Removed the float chamber to check that lift pump was okay.This was okay so refitted, after about 10 mins the engine restarted and was okay for the rest of the journey, condensation could be seen running off the carb onto the drip tray, I have suffered icing only once before but it did not stop the engine, only stopped it ticking over which was a bit of a pain as I was in London at the time. The only difference is that now I use unleaded petrol with an additive, has anybody else suffered since the demise of leaded petrol?. I seem to recall reading somewhere that unleaded is more prone to freezing than leaded so it might well happen again unless someone has a solution. I don't normally take it out under these conditions but the weather deteriorated earlier in the day than I expected

Steve

[Keith Andrews]

Old car technology... expectional conditions...
Humidity very high, temps low, and long run using engine brake and maybe a little lean. the latter can often be picked up if there is the occassional pop from the exhaust.
No I would not put the icing down to unleaded petrol...and there is no need to run additives...
There was no lead begore to war...it was basically introduced into fighter aircraft with superchargers during the war...1 company had the monopoly for the decades.....biggrst rip off of the 20th century, the yk2 bug was the 2nd biggest.
yes lead stops some resession..but the valves guides etc will be well worn before any rescession becomes a problem.
Since old cars tened to get head rebuilt anyway, the industry as general good practice replaced with hardened seats....when unleaded came along, the industry then jumped on the bandwagon recommending even stronger hardened seats (rightly so because then heads would last longer with more rebuilds)...At the same time the lead monopoly trying to keep there multi billion dollar industry afloat put out allsorts of proganda.
Combine that proganda with good practice of using modern hardened seats and a whole mess of old wives tails emerged and remain today.

The biggest issue with old car these days is running very low compression ratios with basically square ground cams (any overlap /duration depends on tappet clearance) on high octane fuels, when orginally theu where designed for octanes in the range of 50 to 70.
Or put another way, its like running a modern car on 110 av gas or alcoloh.

increase octane requirs more lead time on timing cause it burns slower
Also requires higher compression or more accuratly dynamic compression ratio..determined by cam profile
Also requires bigger jets because it has a lower specific gravity, even thu btu is higher by weight. (less by volume.)

Which brings us full circle back to icing up...running lean.

[Forumadmin]

Suffered a lot on some rallies. That is why you fit louvre covers in winter on the Jav or Jup. On some summer rallies in the Alps I used cardboard!

I have seen some mods with water jackets and electric blankets on Jowetts. I also used a system for routing intake air from behind radiator.

[Jorppu]

Carburetor icing can be stopped by adding some alcohol (40 to 1, or something like that) in the petrol tank. Perhaps there are some anti-icing liquids for sale in the service stations. Am I too late with my old fashioned tip ? Everyone knew this already ? At least up here in Finland it is quite common method for carburetor fed engines. Any alcohol (spirit) will do the trick but no use to waste good whiskey. However do not use windscreen washer or radiator anti-freeze liquids. Naturally it would be wise to cover the radiator too. Trust me - I know what I'm doing

[Robin Fairservice]

Living in Northern BC, I soon learnt to cope with things like this. If there is anywater in yopur fuel, gas (petrol) line freezing can occur, and the stores sell "Gas Line Anitfreeze" to deal with this. In cold weather one must realise that there is a vacuum in a carburettor and this will drop the temperature of the petrol/air mixture - hence the possibility of freezing. One secret is don't buy fuel at places that don't sell a lot because there is always a little water at the bottom of their tank, and they may fill their tank infrequently.

[Forumadmin]

Icing was a problem on some of the rallies especially in the Alps. First make sure you are using winter petrol, not that left over from the summer. Winter stuff has better evaporation which you may think would increase likelihood of icing; but it actually improves air mixing and hence fuel to air ratio.
The icing we are talking about here is the contraction of the carb throat with ice caused by the reduction in temperature as the mixture is accelerated through the carb throat. This will also be visible on the outside of the carb as either ice or water droplets. This will throttle the engine and reduce the speed to a crawl. Usually on hill climbs reducing the throttle for a while allows the carb to heat up and power is restored.

Damp conditions increase likelihood of this and it usually does not occur below freezing as water has already condensed out of the air. Typically the worst is a foggy night at 3deg C.

Feeding heated air from behind the radiator and using muffs on the front grill should reduce likelihood.

Remember many old cars had air intake where you moved it in winter to take air from over exhaust pipe.

[Alastair Berney]

I had the same problem several year ago when travelling from Christchurch to Timaru (New Zealand). Several modern cars experienced the same problem on the same night. This was late October when we should have been heading to warmer weather, but on this particular night we struck sleet just beyond Dunsandel and by the time we had reached Ashburton (the half way point between Christchurch and Timaru) we had had to stop several times as the carburettor kept icing up. The carburettor bowl (in the torch light) just looked like a block of ice, but of course with the engine stopped the heat rose up and melted the ice and we were able to carry on again. The motorists with modern cars could not work out the problem, but with us it was quite straight forward, you could see the ice. Luckily the Bradford is not too bad, by my Jowett Seven is much worse. It will ice up on a relatively warm day if there is just a slight cold breeze. I put this down to the fact that the carburettor is directly behind the radiator and is sucking in the cold air straight through the radiator, where as on the Bradford the carburettor sits much higher up and thus is unlikely to ice up in the same way. I know the English winters are more severe than those in New Zealand, but with carburettor icing up I have decided that I will just grin and persevere it.
Alastair Berney
1930 Jowett Seven
1950 Bradford (named Benwillie)
1951 Bradford Woodie
1972 Vauxhall Viva 2300 SL

[Tony Fearn]

[quote="Jorppu"]Carburetor icing can be stopped by adding some alcohol (40 to 1, or something like that) in the petrol tank.

Perhaps 1 alcohol to 40 petrol would be a cheaper alternative.

Tony.