Carb Icing

[squirrel_hunter]

I'm planning ahead a bit...

As I intend to spend next week working on my SV, (sorting the misfire among other things), I was wondering if anyone had any ideas to cure the carb icing problem?

Apart from taking them off, cleaning them and checking the hoses and what-not, is there anything anyone can suggest?

[lynw]

I'm planning ahead a bit...

As I intemd to spend next week working on my SV (sorting the misfire among other things) I was wondering if anyone had any ideas to cure the carb iceing problem?

Apart from taking them off, cleaning them and checking the hose'e and what-not is there anything anyone can suggest?

Dont ride in freezing fog... and if you do, just take it easy. The outside lane of the M25 is not where you want to experience it :oops: :shock: :? :( :lol: .

Discussed this last winter with some of the Selkenters. Ironically, it actually happened on the way home that night to top it off. Carb heaters dont work well apparently.

sorry thats probably not very helpful is it?? :oops: :oops: :oops: :lol: :lol: :lol:

[RandyO]

At least you get carb heaters

[Sid Squid]

The carb heaters do precisely sod all, well, they add a little bit of unnecesary complication and weight, albeit only a small amount of both.

If your bike is affected by carb icing - not all are, and some worse than others - there seem to be only two effective solutions:

1) Fuel additives. Can be dear if you're doing a lot of miles, but probably the most effective way. The most popular variety seems to be Silkolene Pro FST, there are others.

2) Fuel. Shell Optimax has been reported as quite effective, perhaps not as effective as additives, but a whole lot cheaper.

A couple of years ago I made some brackets to lift up the tank about an inch or so, and then ran a duct from the next to the rear exhaust header up into the air filter, this provided slightly warmed air into the carbs and had a very positive effect on carb icing. I didn't go any further with this as I couldn't find a practical way of ducting air under the tank, without having a sizeable tube on the outside of the bike, and tank in my face, but it definately demonstrated that it would work.
Someone else might like to try this, and see if they can come up with a practical duct sizing/routing.

[Scoobs]

I'm lucky that I have not had a problem on my SV, but on my RS125 I could just about manage 20 miles before it packed up. The carb would be encased in thick ice. Fuel additives can help apparently, but as I haven't had the problem (and I do ride all year round) I can't really comment.

[BillyC]

I still don't understand how your fuel can make a difference to carb icing. Classic carb icing anyway. This is probably because I'm not familiar with the construction of the curvey SV's carbs.

I get caught into this argument about once every six months. It's been a while, so here's my money's worth again.

To understand carb icing, you must appreciate two principles:

1 - Air can sustain a given amount of born water. You probably know this as the humidity of air. The warmer the air, the more water it can support as vapour. Air at 15C and 100% humidity, may contain the same amount of water as air at 20C and only 60% humidity.

2 - Charles's Law. This clever chappy noted the relation between the volume of a gas, and its temperature. If you cool a gas, its volume decreases. Alternatively, if you compress a gas, making its volume smaller, its temperature falls.

Carb icing occurs when cool, but moist saturated air is being drawn into the carb.

As the air enters the funnel of the carb, it is compressed and starts to travel faster. Because it is being compressed, Charles's Law says its temperature also falls.

As the temperature falls, the air can no longer support the moisture that it holds, and water droplets condense on the inside of the funnel. The air temperature may fall significantly enough, so that as this water condenses, it instantly freezes.

The ice created forms a build up on the inside of the funnel. This makes the funnel smaller, meaning that the air drawn in is compressed even more - and with that the cycle gets stronger and stronger - colder and colder, more and more ice forms.

This all happens long before fuel has entered the equation.

The only really effective way to combat carb icing, as Emperor Squid has mentioned, is to introduce warm air to the air intake. The temperature drop does not take the air below freezing - therefore no carb icing.

I guess some kind of heat-pipe could be set up between the exhaust heat and the carb funnels, but that might just take the icing elsewhere. The other possible solution would be an alternative airbox, which instead of taking a direct feed of air from the cold air around the fuel tank, takes it from arond the rear exhaust port - but I think this is what Mr Squid suggested anyway.

[TSM]

What about having a waterproof heating element in the airbox, that is temp controlled?

[BillyC]

What about having a waterproof heating element in the airbox, that is temp controlled?

Possibly... but remember your airbox is only plastic, and in many cases the air filters are made of paper. It also sits just under a great big tank full of petrol :lol:

It would have to get warm enough to heat the air, and still not be a fire-hazzard. You'd have to wire it in with switches and thermostats.

I'd rather just duct a hose that warms its contents over the engine.

[paul cooper]

Oh dear
Slight misunderstanding here, I am not be pedantic, but there is a fundemental flaw in Billy's explanation-------. When gas is compressed, it heats up, when it expands it cools (aka refrigerator). When fuel & air mix (in the carb), the petrol evaporates, which takes heat. The heat has to come from somewhere & the carb being metal (says he not even knowing if they are on the SV), conducts heat very easily. When the ambient air temperature is warm (say +5 degrees), there's enough heat to go around. When the temperature is cold (say l< 5 degrees), then the evaporation process still requires the same heat, then things start to get dragged down in temperature, the carb gets to a temperature below the freezing point of water & guess what, the water in the air starts to freeze on & probably in the carb--------- There are times I wish I wasn't an engineer, I'd probably earn more money & wouldn't find myself writing sad E mails!!

[jambo]

Sorry Billy, with Paul on this, Gas heats when compressed

[BillyC]

Paul,

I'm not wrong, I just didn't go into significant detail as I've got better things to do.

The significant factor is that as air enters a carb, it's temperature falls. No argument, it does.

You cannot compare a carb to the heat exhanger of a refrigerator, they're not the same thing. Also, latent heat doesn't come into it, which is the main principle behind refrigeration.

Air flowing into a carb has to occupy a smaller space (is compressed), has to flow faster to occupy that smaller space (the pressure drops), and as the volume's pressure has dropped, it's temperature also falls.

[BillyC]

Sorry Billy, with Paul on this, Gas heats when compressed

Gas heats when compressed and volume decreases... but we're not using a pressurised container, we're moving air along a pipe.

[paul cooper]

Ah well, we won't argue about it.
It's good to see lively debate, which I sure will continue
Paul

[BillyC]

Ah well, we won't argue about it.
It's good to see lively debate, which I sure will continue
Paul

No lets :lol: we're just arguing about the same thing :lol:

If you're an engineer, then you'll appreciate there's lots going on at the funnel end of a carb. Air is inducted, and forced into an funnel that is constantly decreasing diameter tube (my confusing compression and volume suggestions related to this). In order to continue through this tube, the air must travel faster.

As air travels faster, its pressure actually drops (Bernouilli Effect), and so does its temperature. Hence carb icing.

You want the pressure to drop, because that's what allows the fuel to be introduced into the air, and vapourised.


Jambo, the fundamental difference here, is that we're talking about flow along a pipe, not an enclosed system, that you might find in a syringe, or a fridge :lol:

[jambo]

I agree with the fact that as the air travels faster the pressure dropps and so does the temperature.

I'm fairly sure we're all pretty much using the same argument from different view points so all is well with the world! 8)

[BillyC]

...so all is well with the world! 8)

No it's not ;)

But all is well with the Forum. :lol:

[paul cooper]

Oh OK then lets
The basis of carb icing is evaporation of the fuel, evaporation needs heat, it takes heat from wherever it wants. when the ambient temperature is low, it still takes the same amount of heat, causing freezing of the water droplets.
There's tons more to fluids flowing through pipes, being compressed or not it, but it's evaporation that causes carb icing
There, now we're arguing, fun isn't it
Paul

[BillyC]

Oh OK then lets
Excellent :D
The basis of carb icing is evaporation of the fuel, evaporation needs heat, it takes heat from wherever it wants. when the ambient temperature is low, it still takes the same amount of heat, causing freezing of the water droplets.
There's tons more to fluids flowing through pipes, being compressed or not it, but it's evaporation that causes carb icing
Well that's one way of looking at Carb icing. The latent heat evaporation of fuel. I'd not considered that, and I welcome your new information.

If that's the way it works in the SV, then so be it. I can certainly see how changes in fuel or adding additives would affect that kind of icing.

The kind that I've described, is what is taught to pilots all around the world, and is essential knowledge when flying any piston engine aircraft. That's how I learnt the detail of it, but originally covered the theory in A-level physics. :?

I'd certainly consider my version of events to be the classic and common form of carb icing! :wink:
There, now we're arguing, fun isn't it
Oh yes! :lol:

[Scoobs]

There, now we're arguing, fun isn't it
Oh yes! :lol:

I don't know whether to say "get out more" or "get a room"?

[BillyC]

There, now we're arguing, fun isn't it
Oh yes! :lol:

I don't know whether to say "get out more" or "get a room"?

Scoobs, control your jealousy!

[Scoobs]

Scoobs, control your jealousy!

Thats all it is Bill, that's all it is! :lol:

[muddycoffee]

I've seen 4 cylinder bikes, more than a decade ago which had their carburetters changed by Kawasaki to prevent carb icing. The new ones had small pipes around the outside two them which were plugged into the the cooling system, which transferred engine coolant heat to the carbs, which kept them warm enough to stop icing.

This was a general recall, and a mate of mine who worked at a Kawasaki dealer had lots of spare old original Carbs to mess about with.

[squirrel_hunter]

Ok, so I need to keep the tempature of the air up. A heater in the air box is ruled out and a pipe from the exhaust isn't very practical. So how do I modify the existing carb?

What would larger heater hoses do, and would this impact the cooling system in other areas? Runners get given silver foil at the end of a race to keep body heat up, is anyone thinking what I'm thinking?

And what about a new carb entirely, what would bolt straight on, or is this out of the relms of practicality? Finally Why do some bikes or some SV's suffer more than others?

[Sid Squid]

What would larger heater hoses do, and would this impact the cooling system in other areas? Runners get given silver foil at the end of a race to keep body heat up, is anyone thinking what I'm thinking?

The SV carb heaters are electric, not hoses running out of the cooling system.

And what about a new carb entirely, what would bolt straight on, or is this out of the relms of practicality? Finally Why do some bikes or some SV's suffer more than others?

Well another carb in the same circumstance would suffer the same temperature conditions, as for differing degrees of carb icing that's down to the specific circumstances of use, and the fuel used, thus any additives the producer may use.

I worked for a Kawasaki dealer when there was the recall for many models because of carb icing, as I remember it all that was replaced in most circumstances was the float bowls, which were replaced with ones having water ways in them and tee pieces inserted into the cooling system to supply them, in a similar way as does my modern Kawasaki.

[muddycoffee]

The SV carb heaters are electric, not hoses running out of the cooling system.

Excuse my ignorance but do all SV650 models with carbs have these electric heaters? I've not had mine for that long and I haven't really taken it to bits enough in that section yet?

Mine is a Y, the one before K..

[Dicky Ticker]

Drop and extend the air intake ducts behind the radiator and get aviation fuel which is devoid of the same quantities of moisture as normal petrol

Resulting in warm air intake and moisture free fuel-------might work

[Sid Squid]

Excuse my ignorance but do all SV650 models with carbs have these electric heaters? I've not had mine for that long and I haven't really taken it to bits enough in that section yet?

Mine is a Y, the one before K..

As far as I'm aware the only bikes that have carb heaters are official UK spec bikes, parallels won't have them.

And only curvies obviously. :lol:

But it doesn't matter 'cos they don't bloody work anyway.

[Sid Squid]

Drop and extend the air intake ducts behind the radiator and get aviation fuel which is devoid of the same quantities of moisture as normal petrol

Resulting in warm air intake and moisture free fuel-------might work

See my previous post, maybe back a page or so. I ducted from next to the rear exhaust header, which worked well enough, but simply it wasn't really practical - I couldn't think up a suitable route for a big enough duct, it may be possible though, I didn't try that hard.

Most of the icing is from airbourne moisture, not from the fuel, this why we get carb icing at certain temperatures only, when it gets really cold it's rarely a problem as the moisture recondenses out of the air and never gets to your carbs in the first place.

[embee]

The temperature drop comes predominantly at small throttle openings where the incoming air is being expanded into a low pressure region after the throttle. The sudden pressure drop encourages the evaporation of the fuel which drops the temperature further.

It isn't absolutely essential to have the fuel evaporation bit to get icing (though it makes it a lot worse), most fuel injected car engines have heated throttle bodies mainly to prevent breather icing even though the fuel injectors are a long way downstream. Crankcase breather gas is made up mainly of water and CO2 (it's effectively the same as exhaust gas), so even if the atmospheric humidity is low you can still get serious ice build up.

Sid's route of heating air for the intake is a well tried and tested method, most carb car engines had some sort of hot/cold air switching taking hot air from round the exhaust manifold. Many had a waxstat controlled flap to limit the hot air temp (you can get as much problem from having carbs getting too hot, fuel vapourising in the floatbowls etc). It wasn't always totally succesful mind, old Minis were notorious for suffering carb icing even with the hot air off the manifold.

I don't know whether some form of diverter to take air from behind the radiator would be enough to make much difference. Trouble is it would only work at all once the thermostat was open and the rad was hot anyway.

Fuel additive is the simplest.

[Richie]

I did a Cryogenics, High pressure, pure air Systems course back in 1999 mainly using the Joule-Thomson effect ... High pressure air being released into atmospheric pressure through a small hole or nozzel, the tempreture of the air (gas) drops drasticley.. that the principle of how thermal image sights work.
now as i see it, a Carburettor has a venturi. where the air passes through the venturi it gathers great speed to atomize the fuel and also as a result of the increase of speed it reduces the air pressure, there fore the air temp reduces and as Billy says the water vapour in the air turn to ice..
thats when you can get carb iceing.

I think that's it...Carburettor icing caused by the sudden temperature drop due to fuel vaporisation and pressure reduction at the carburetor venturi. The temperature drop of 20-30°C results in atmospheric moisture turning into ice which gradually blocks the venturi. This upsets the fuel/air ratio causing a progressive, smooth loss of power and slowly strangles the engine.

[Moo]

I remember reading an artical in one of the bike mags a few years ago on carb icing they waffled on for two pages only to say that the only real way round the problem was to by a fuel injected bike. :lol:

[Richie]

I remember reading an artical in one of the bike mags a few years ago on carb icing they waffled on for two pages only to say that the only real way round the problem was to by a fuel injected bike. :lol:
yep my Quack ZZR600 suffered drasticley from carb icing, but my K3 SV does not.. :D

[Anonymous]

I can deal with the icing.....it's the marzipan I don't like.

[Sid Squid]

But my carburetted ZX6 never does, go figure.

And I quote: It's all bollox innit.

[21QUEST]

Can't say I've suffered from carb icing but must say some of the definitions why or how it happens are not strictly B.A.S.A.T compliant :) :wink:

More later :wink:

Cheers
Ben

[Cloggsy]

...it's the marzipan I don't like.

Ditto :sick:

[21QUEST]

Memory not as it used to be but every now and then it gets jogged :) .

The following text is definitely BASAT compliant 8) :wink:



The scanned pages are from Fuel Systems , Tech Book by John Robinson(page 1.4 -1.5).


http://img370.imageshack.us/img370/6043/carb11on.jpg



http://img384.imageshack.us/img384/9684/carb26kd.png

Hope this has straightened out things.

Cheers
Ben

[BillyC]

21QUEST, that's all very well if the icing happens in the region of the fuel jets. However, that's not always the case.

Carb icing often happens no where near the jet or where the vapourisation occurs, and this is something you have to consider when heating a carb. It may be all very well keeping the fuel warm, but if the icing is happening long before that, they it's not much good is it.

[paul cooper]

I've changed my mind now anyway, I like the marzipan explanations, far beter than all the technical stuff. I got the ideal cure for it, I don't ride the thing when it gets cold!!!!!, I have done & I know it's prone to marzipan, especially when you've had the throttle open for about 10 mins & come to a junction, stupid thing backs right off when you go to acelerate & then starts to cough a bit. Can be quite off putting
Paul

[RandyO]

I get classic carb icing in fall & spring, the best thing I have found to do is ride untill the bike starts to sputter, then I stop for a few minutes with the engine turned off, and allow heat from the engine to transfer to the carbs, after a few minutes sometime I have enuf heat transfered that I have no problems for the rest of the day, other days, I have to do that several times

[squirrel_hunter]

If the problem is that there is not enough heat getting into the carb and the heaters on the bike aren't upto the task is it possible to get some sort of replacment heater or to piggy back whats already on there?

[RandyO]

Drop and extend the air intake ducts behind the radiator and get aviation fuel which is devoid of the same quantities of moisture as normal petrol

Resulting in warm air intake and moisture free fuel-------might work

warming the air up will not prevent carb icing, you have to warm the body of the carb

carb icing is basicly the same thing as choking the carb, ice builds up in the carb and reduces the amount of air that can pass.

the ice that builds up is from the humidity of the air and nothing to do with fuel

[northwind]

Here's the thing though, with SVs you can literally have 2 bikes parked side by side and ridden over the same journey in exactly the same circumstances, one suffers icing and the other doesn't. I've never suffered it at all despite doing a lot of riding in absolutely prefect icing conditions, which makes you wonder- why not? Why is it that one bike has problems while another powers on?

I don't have any actual solutions, natcherly :) Although one thing you see mentioned often is to move the sensor for the carb heaters- sometimes it ends up stuch somewhere warm and so fails to switch them on. Checking the wiring and connectors could be worth doing too- thpugh I tend to agree that they're pretty much irrelevant.

If I suffered it, I'd be looking at borrowing someone who doesn't suffer it's carbs... I know that logically that should be no difference, but something does, and logically it's got to be in the intake side of things.

[alongwor]

Am I right to assume this icing issue restricted only the carbed versions of the bike and the later fuel injected versions are fine?

Andy.

[mysteryjimbo]

Am I right to assume this icing issue restricted only the carbed versions of the bike and the later fuel injected versions are fine?

Andy.

Yup.