I know this may seem like a random question, but under the right conditions is it possible for a carbed or single point injected intake system to develop carb ice?

I know its a problem on methanol fueled drag cars, but thats a different matter! However, i dont know of an issue with it on normal carbed engines

It happens on my mini, and can be a bit of a pain as it won't run right at low revs. This is on a near full race engine though, so don't know how it'll affect a "normal" engine.

Fairly unusual on a modern engine & easily solved by providing a hot air pickup fromthe exh manifold area

1990's Kawasakis were terrible for it.

Thats why they run the engine coolant through them!

Steve

I had a cavalier sportshatch with an aftermarket carb (weber replacement for autochoke)
It had aa asbestos type spacer which if fitted in winter allowed the carb to ice up after about 25miles (flooded itself)
If you left the spacer out it would boil the fuel bowl dry when turned off and you'd need to crank it over to get it full again before it would start.
So yes it is possible.

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Originally posted by tegwin
I know this may seem like a random question, but under the right conditions is it possible for a carbed or single point injected intake system to develop carb ice?

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The only reason I ask is that I fly helicopters occasionally...

It is powered by a 5 litre boxer engine (200 odd HP)

It runs on 100 octaine fuel and has a normal carb on it....

This monster really does suffer from serious carb ice if you dont adjust the heating of the intake air...

I was just curious if cars suffer from a similar problem if you use an intercooler and a turbo for example on a carbed engine....


For those that dont know...carb ice occurs in venturis where the air pressure changes causing the temperature to drop hence the ice...this ice freezes the butterfly valves and constricts the airflow into the engine and has caused many crashes...

Edited to say:
WOA....5 replies in the space it takes me to type a response...I guess the above question is answered

[Edited on 15/11/06 by tegwin]

I stand corrected

I managed to get ice on the inside and outside of the inlet on the mini. You could take the bonnet off and see the white patch on the bottom of the inlet, which was also the bit closet to the exhaust! It was were the manifold bent towards the ports though.

It used to happen in cold foggy conditions on my Standard 8 (some time ago now )
When it happened, you could see frost on the outside of the carb (downdraught Solex I think)

A bunch of us were going back to Glasgow from Perth at night and I left a few minutes before the others. I ran into fog, the carb iced up and the car went slower and slower. It was a bit worrying thinking of all my mates barrelling along through the fog behind me. A handy layby saved the day. Stop, let engine heat thaw out the carb and off again. Change underpants once home.

If this is an issue with a standard carb...how can you get away with running a turbo and and intercooler...pre cooling the air and ramming it in is only going to make the icing conditions worse...... How does this not kill the engine?

(the only logical solution is to warm the air with a bleed from the exhaust...but doesnt this defeat the object of an intercooler?)

Carb icing is reltaed more to humidity than temperature.
essentially there are two types of carb icing, the first is "fuel ice" and forms downstream of the jet that introduces the fuel into the venturi. As the fuel is vapourised the temperature reduced and if the temperature falls below freezing point any water vapour in the airflow will freeze and the ice will impact onto whatever is in its path.
The other type is kmown as "Throttle ice", as the air /fuel vapour accelerates past the butterfly ( at small openings) there is a temperature drop due to the reduction in static pressure which can cause throttle plate ice forming.
This effect is not a function of temperature alone, in fact it can occur at quite high temps if the humidity is correspondingly high. Conversly at very low temps the humidity is very low and there is no water vapour to freeze.
Expect it to generally occur at 5-10 degrees celcius and moist conditions.
Adding heat to the incoming air and or the carb/manifold is the cure.
Longwinded or what!
Hope this helps

Regards
Dave

[Edited on 16/11/06 by Dave-M]

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Originally posted by tegwin
The only reason I ask is that I fly helicopters occasionally...
[Edited on 15/11/06 by tegwin]

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Common problem on V.W. Golf, Scirroco , Polo Etc with carbs also the old air cooled . Caused by faulty/ missing pre heat pipes /valves etc. Happened to me on way to SVA in May of last year . Was cold though

I had problems with mine at the beginning of the year. If temperatures dropped below 1 or 2 degrees and it was damp, the car would misfire badly and bog right down. As soon as I got into the warmer / dryer / sunnier air, it would pick pack up again.

I diverted the thermostat overflow to header tank pipe to go through a brass pipe though my carbs. The problem went away. Carb icing? Maybe.

It's more common on flying stuff due to long descents from lower temps (there is an "icing level" broadcast as part of aviation weather each day, which is where the dewpoint & temp are the same) on low throttle, hence why you have to pull carb heat on when shutting down throttle. This has been done automatically on cars for years now (at aslight performance sacrifice) hence icing only usually occurs if there is a fault with the system.
The Kawasaki prob was well known, but again was exaccerbated by the waterway which was supposed to warm the carbs, becoming blocked, hence little or no flow & no warmth. I've never had icing on my Kwaks but then it gets so hot under my engine cover you could fry eggs on it!

quote:

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Originally posted by omega 24 v6
I had a cavalier sportshatch with an aftermarket carb (weber replacement for autochoke)
It had aa asbestos type spacer which if fitted in winter allowed the carb to ice up after about 25miles (flooded itself)
If you left the spacer out it would boil the fuel bowl dry when turned off and you'd need to crank it over to get it full again before it would start.
So yes it is possible.

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quote:

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Originally posted by tegwin
If this is an issue with a standard carb...how can you get away with running a turbo and and intercooler...pre cooling the air and ramming it in is only going to make the icing conditions worse...... How does this not kill the engine?

(the only logical solution is to warm the air with a bleed from the exhaust...but doesnt this defeat the object of an intercooler?)

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I'd love to have a problem with my intercooler being so efficient that my supercharged ST1100 starts icing.
Sadly I think it will be the other way round- that power gains will be ofset by high inlet temperatures, meaning the timing gets backed off, loosing any power increase.
Oh well, at least the supercharger will sound cool

Hmm..I didnt realise that turbos and superchargers got the air temp that high....no wonder the intercooler couldnt ice the air...

This brings me onto another question....

It is fair to say that the hot air from the turbo/super is cooled in the intercooler to give a slight power gain to the engine....

Could you gain even more power by dropping the air temperature much more and by removing the water vapour by passing the air through an aiconditioning type device driven by the engine.. (yes the aircon compressor would use power from the engine but would the gain in power be more than the loss?)

Such a random question but its interesting...

Fuel system icing inhibitor can be added to most aviation fuels, The RAF uses it all the time, If a fuel is uplifted from an unsure source then the tanks have to filled and flushed on large transport aircraft.

I believe it can be brought as a seprate additive but you'd have to check the manufactures recommendations.

ATB Dan.

My R1 ices up the front carb when it's cold. The slide sticks, and if you stop and whip off the air filter quickly you can see the ice!

I'm not fussed about - if it was still in the bike I would be though!

quote:

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Originally posted by tegwin

Could you gain even more power by dropping the air temperature much more and by removing the water vapour by passing the air through an aiconditioning type device driven by the engine.. (yes the aircon compressor would use power from the engine but would the gain in power be more than the loss?)

Such a random question but its interesting...

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If an intercooler can cool the air significantly wouldnt a bigger decresae in temp be seen if the intercooler was wrapped in the cool aircon stuff?

I'm no expert, but i think its a case of diminishing returns.

The pump would load the engine,decreasing BHP...fit a bigger pump to get better cooling...etc,etc.