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george
United Kingdom
862 Posts |
 Posted - 08/02/2012 : 16:18:58
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| Back in the sixtys when I was learning to fly my instructor known as mother [because we thought he was an old woman] took great pains to point out the perils of carb icing ,we went through the checks and did as we were told.I started up the N yesterday and watched in fascination as first the butterfly area then the whole of the inlet area of both carbs turned white and crystaline .It persuaded me that with only aeroscreens it was too cold for a drive.See mother did know best Geoff ps reading the float chambers whilst watching I read that the SU company spell the name of the product with er at the end I always use or, my OED says both are good |
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Mike Allison
United Kingdom
196 Posts |
Posted - 08/02/2012 : 16:36:11
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Yes, George:
carb icing has always been a problem with "our" cars. If the air temperature is around 0 degrees C, and the humidity is above 60% it WILL happen. I had it on my P and F types when we had those bad winters (the Thames froze over at Teddington in '63!) Even the 18/80's I had suffered!
Those who run supercharged cars will suffer with it, especially if the blower is mounted in front of the radiator.
Now I am past seventy I wait until the air temp rises into double figures!
Roll on spring,
Mike
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Bob Stringfield
United Kingdom
854 Posts |
Posted - 08/02/2012 : 18:52:01
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Carburettor icing is a problem with older flat-twin motorcycles such as the LE Velocette, where a single centre carb. feeds down a long external manifold to widely separated cylinders.
Informed makers kept the manifold and carb. warm inside the engine casings as far as possible. |
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Oz34
United Kingdom
2527 Posts |
Posted - 08/02/2012 : 19:16:46
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Yes Mike & I heard there were ice floes off the Sussex coast. I kept well away from the sea so can't confirm!
Hopefully Geoff, Mother impressed on you that you can get carb icing with an outside air considerably above freezing? humidity is the important factor.
Dave |
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george
United Kingdom
862 Posts |
Posted - 08/02/2012 : 20:05:02
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| In his defense mother was a good bloke taught me well ,kept me safe through a 35 year career but OMG the halitosis Geoff |
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Oz34
United Kingdom
2527 Posts |
Posted - 08/02/2012 : 21:52:35
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A career sounds a bit more than PPL?
Dave |
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Rodney Collins
United Kingdom
424 Posts |
Posted - 12/02/2012 : 13:26:28
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The late Paul Duncombes put a well engineered cure for front mounted supercharged TTT M's,on the TTT M web-site. He designed it after he had suffered from the problem. I never got round to making up his system, but if there is anyone out there who wishes to drive their S/C car in cold weather look up Pauls answer to the problem.
Rodney |
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Gordon
United Kingdom
691 Posts |
Posted - 12/02/2012 : 17:19:33
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Rodney,
I am having difficulty in finding the reference to Paul Duncombe's carb icing solution. Could you, or anyone, point me in the correct direction to this information please.
Gordon
PB 0331
MG 4473 |
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spitfire
United Kingdom
371 Posts |
Posted - 12/02/2012 : 20:33:00
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Has anyone used a product
Silkolene PRO FST?
It is put in the fuel at a 1-2% ratio and helps stop carb icing, stabilises fuel when long storage and generally cleans what it passes through.
Used on motorcycles and performance cars. The square rigger cars have the carbs right next to the elements, not sat within the confines of an engine bay. |
Edited by - spitfire on 12/02/2012 20:34:24 |
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David Allison
United Kingdom
665 Posts |
Posted - 13/02/2012 : 09:40:37
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Silkolene FST is a product developed for motorcylcles - basically it is an oil based product added into the fuel to reduce the risk of the water in the fuel separating out and icing inside the carb.
The most effective way to combat carb icing is to limit revs and sustained throttle openings on really cold days.
Just an excuse to blat along B roads rather than motorways.
Also avoid driving across high downlands and North Yorks Moors in the dead of winter.
I do remember an event some years ago in the Peak District in May when we were hit by a sudden snow storm - driving the car on the ignition switch on a downhill section because the throttle was stuck in the half open position.
There is no really hard bitten "CURE" for carb icing - it even happens on moderns.
However the modern motorcycles have heated carb bodies which do prevent it to a degree.
The colder the air and the higher the speed - the more likely you are to get carb icing.
Regards David |
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Rodney Collins
United Kingdom
424 Posts |
Posted - 13/02/2012 : 10:50:57
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Gordon
Paul's system used hot air from the manifold to heat the carb, he told me that after he fitted the system he never had the problem again. He put a full discription and diagrams on the TTT M website it must have been 3 or 4 years ago. I am sure it must still avaliable, perhaps Nick could guide you to it. Paul was a very accomplished engineer and his system was very proffesional in both looks and function. I hope you can find it.
Regards
Rodney |
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Bruce Sutherland
United Kingdom
1561 Posts |
Posted - 13/02/2012 : 11:31:18
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For those interested in the late Paul Duncombe's warm air feed & controls to his front-mounted supercharger, ever courteous, Paul allowed me to take photos of this at Silverstone 2007:
I hope these help.
Bruce. (PB0564) |
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Gordon
United Kingdom
691 Posts |
Posted - 15/02/2012 : 08:19:16
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Bruce,
Thanks for posting the photos which are a great help.
Rodney,
I have searched all Paul Duncombe's posts on all the forums and not found the info you refer to. Nick Feakes suggests that it must be in some other place and has suggested the Yearbooks.
All,
I would be very grateful if anyone with the back issues has the time to search for Paul's article and tell me where I can get a copy please. Or any other suggestions!
Gordon
PB 0331
MG 4473 |
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Dow
United Kingdom
490 Posts |
Posted - 15/02/2012 : 09:14:50
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I am almost certain that Pauls article appeared in the MMM Bulletin prior to Nov 08 (the ones after this date are on this site and do not include his description of his solution to the Icing problem). I cleared my old Bulletins out a few months ago.
Regards
David D |
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David Allison
United Kingdom
665 Posts |
Posted - 15/02/2012 : 09:29:12
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It is an interesting idea - taking inlet charge from around the exhaust down pipe - the works did a similar thing on the K3 prototypes for the Mille Miglia trials (which were over the winter), a pipe from the carb intake was directed up to the top of the radiator and took warm air from there.
I understand that the idea did not catch on because it actually made the problem worse.
The warmer charge actually condensed more readily because of the temperature difference in the venturii and caused icing.
Paul's idea was interesting in that he could use a lever to change were the carb got its air - ambient air coming in through the front mounted inlet and warm air from the back.
Paul was able to alter the opening of both apertures to control the amount of hot or cold air.
He told me that in fact he never really had the time to try it out in properly cold weather.
Many K3's and also NA 0307 were fitted with an air filter - this was developed to help stop stones going into the blower but also did go a little way to preventing really cold charge air going directly into the carb.
My father found though that the engine became sensitive to mixture on warm days and ran too rich - discussing it with Jacko the advice was "throw the bloody air filter away!"
Modern air filter products have improved things a great deal and actually if you can get a filter in there it is probably a good idea.
Modern thinking is the heat the carburettor (air intake) body with coolant from the engine - this raises the temperature of the venturii and reduces the risk of ice forming.
A sage freind of mine in the motorcylcle tuning world says that neither system works - even fuel injected bike engines sometime suffer with trouble in cold weather!
He advises just using a bit less throttle in cold weather.
My experience of throttle icing is that you can normally drive round it on the road - it is all part of the "joy" of driving these old cars.
Racing it is a bit of a chore - you can even have it happen in summer - lift off the throttle and it is stuck wide open JEEPERS! - but you get used to it.
On the highly supercharged NO special (NA 0995) we always used to blank off the blower cowl with tape - it didnt look very nice but it did help.
On an unblown MMM car it is normally a sign of too much ignition advance and over weak mixture - another issue would be water in the fuel.
If the car is going to be laid up for long periods you should really drain the fuel tank and fuel lines anyway.
Funny how the development of a 1930's car has parallels though in a modern world for a problem that has blighted the internal combustion engine since the begining.
Perhaps the oddest thing is that the only "cure" seems to be the one advised in the 30's - Slow down a bit in cold weather.
Yours with a smile David |
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george
United Kingdom
862 Posts |
Posted - 15/02/2012 : 09:50:03
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| Going back to the start of this thread my quess is that the system we used all those years ago on little aeroplanes would be similar to the one on the immaculate P up the page .All we had was a simple push /pull control ,in for cold air out for hot used when mother thought fit Geoff |
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