Carb icing? How to fix?

[D O G]

Reet, need a bit opf advice and assistence from you fine folk...

I think the bike is suffering carb icing, symptoms are that when the air is cold (like this morning), it runs very poorly at low ish revs - like only on two or three cylinders.

I need to rev it loads to stop the misfiring, but it is only a temporary 'fix'. It has happened several times in the past on long, cold motorway runs - where the bike would misfiure and bog down briefly when I wind on a bit more throttle.

This morning, however was so bad that it was cutting out (revs would just die off) if I wasn't on the throttle and above arounf 5k revs.

It was a bit of a pain filtering down a hill, with the clutch in, half throttle to keep the revs up, and keeping speed down with the rear brake

Questions are;

1. Does this sound like carb icing?
2. What is carb icing?
3. How doe I fix it? (Strip and clean carbs was my thought?)

Thanks in advance!

[Dalemac]

Sounds like carb icing to me, my gpz got it bad today too, its in the dealers now, where its getting a good clean and balance.


I dont know what it is, but at a guess i'd say its when the carbs are cold.

On the gpz coolant from the engine is supposed to run into the back of the carbs to keep them warm, thus getting rid of carb icing, mine is clearly suffering from carb icing, and hopefully a clean/ service of the carbs will sort it out.

Sorry i cant be loads of help, but i can say that it definately is carb icing.
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YBR125 -> GPZ500S -> SL1000

[Kickstart]

Hi

Not so sure it is.

Carb icing is due to the carbs being so cold that they freeze the moisture in the air as it goes through the carbs, causing lumps of ice to block various jets. Cold air going through at speed takes heat from the carbs. As such it needs pretty cold but damp conditions to occur (fog is probably the worst conditions). Too cold and there is not enough moisture in the air to cause a problem.

Problem tend to be caused by running at speed as the airflow through the carbs is far greater, taking more heat from them. Although the results are less noticeable at speed.

Running at low speed / idle / stopping for a while will likely cure the problem for a short while as the engine heat will soak up into the carbs. Keeping the revs up is likely to make the problem worse and longer lasting.

There is no real easy fix. There are additives that you can use to reduce the problem. You could try other brands of fuel. The production fix is to fit carb heaters (either passing warm engine coolant through the carbs to heat them up, or an electric heater), but not something you can easily do yourself. With carbed cars the easy solution was to have the airbox intake pick up warm air from near the exhaust in winter.

Kawasaki spent a fortune 15~20 years ago recalling all the liquid cooled 4 strokes they had sold in the UK and fitting them with carb heaters (and that meant fitting new carbs to all the bikes). Hate to think how much that cost them.

All the best

Keith
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Traxpics, track day and racing photographs - Bimota Forum - Bike performance / thrust graphs for choosing gearing

[D O G]

I vaguely recall that the bloke who dyno'd it about a year ago said that as it was an import it had the carb heaters - or was it the other way round? Hmmm.

I have never cleaned the carbs in the 14months and 9000 miles I've owned it would this help??

[Kickstart]

Hi

Import might well not have carb heaters.

Cleaning them will probably make little or no difference.

All the best

Keith
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Traxpics, track day and racing photographs - Bimota Forum - Bike performance / thrust graphs for choosing gearing

[The Tot]

I thought it was a problem endemic to Kawasakis. If it's cold, misty and your bike is bogging down despite constant throttle + adding more throttle at a constant speed, it probably is carb icing. It often does happen at instances where you are at constant throttle opening, i.e. motorway. Had this happen to me up the M1.

Unless it could be your reg-rec/ignition system too. My 250 had similar symptoms what you described but in the mild spring. But seeing that it is winter, carb icing could be the culprit. Silkolene FST seems to alleviate the problem = 10 quid for bottle (1l i think). and it's something like 100ml to every litre of fuel.

Cured the symptoms in the winter - i rode up from brighton to london in mid winter last year in the cold and mist and was fine on the kwak 250.

Although, if you use the search function - everybody last year was diganosing their problems as carb icing when it wasn't, since very few actually had a grasp of the problem.
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[Ichy]

Personally I would try spraying the electrics, especially the plugs and coils with ignition sealant or, at worst, WD40. Just make sure all is dry first.

Condensation, caused by cold weather and warm bikes, can cause all sorts of weird problems.

[stinkwheel]

Carb icing. So you need an engineering solution that will increase the circulating water temperature by altering the thermal dissipation characteristics of your engine in its entirety thereby allowing increased transfer of heat energy between the engine and the carburettors.

But what system could be so feindishly complex yet able to be produced at a reasonable price and be easily fitted and removed by your average motorcycle owner? Could there possibly be such a system within the realms of modern technology It seems insurmountable but I suppose I'd better have a crack at a solution....

Block off half your radiator with a bit of cardboard.

There you go. No charge.
____________________
“Rule one: Always stick around for one more drink. That's when things happen. That's when you find out everything you want to know.”
I did the 2010 Round Britain Rally on my 350 Bullet. 89 landmarks, 3 months, 9,500 miles.

[D O G]

Genius Stinkers, I will try that. If it works, I owe you one, if not, I will hate you for EVER.

[stinkwheel]

You asked how it works too huh?

Lick your finger and blow on it. Feels cold right?

No imagine that effect magnified by fuel vapourising in fast moving air passing through your carburettor. That's going to be pretty cold yeah? Now imagine the whole effect being concentrated on the end of the throttle needle.

It's not a great step of intuation to work out that this could easily reach the point where the temperature at the tip of the throttle needle gets to below freezing point. This isn't a problem in itself because petrol freezes at a massively low temperature.

What does cause a problem is if that temperature reaches below freezing and there is a high level of air humidity. The moisture coming in with the air freezes on the tip of the throttle needle forming an ice crystal which blocks the main jet preventing fuel getting through.

That's why you tend to get a problem with it on cool, misty mornings/evenings. Not such an issue on frosty mornings because there is usually a clear sky and as such low humidity.

I have long suspected Kawasaki have such a problem with this because of their highly technical airbox design (some kawasaki airboxes can deliver up to 120% of the engine displacement in air per revolution due to pressure wave reflections). I have visions of small clouds of water vapour forming inside the airbox as the pressure waves collapse. Be interesting if someone put a camera in there.
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“Rule one: Always stick around for one more drink. That's when things happen. That's when you find out everything you want to know.”
I did the 2010 Round Britain Rally on my 350 Bullet. 89 landmarks, 3 months, 9,500 miles.

[TUG]

stinkwheel, does it effect some bikes or all or most? i've not had a problem like this on mine and the other day it was really frosty out.
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Haz ER-5, innit!

[stinkwheel]

[crazymotorbik...]

Hey,

Pro FST works great for carb icing. My GPZ305 was a bitch for running very rough in the winter. Two caps of Pro FST to a tank of petrol made a world of difference

Cheers,
Shaun.

[cagiva gezzer]

I agree with all the "Silkolene Pro FST" comments.

The way to help rule out carb iscing is that it doesn't happen when it's really cold (Minus temps) as the air is much drier.
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"because one stroke isnt enough and four strokes waste two"

[Kickstart]

[Ben.]

how do you know whether its carb icing or not? common symptoms? Any way to tell?
____________________
follow my racing season
Race bike - R6
Road bike - sv650

[Kickstart]

Hi

Very rough running and stalling in cold (but not VERY cold) damp conditions. Increased fuel consumption. Unlikely to be a problem from start up or while running round at low speed. Likely to start after going at speed, and take a while to clear.

On some bikes you may even see frost formed on the outside of the carb.

All the best

Keith
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Traxpics, track day and racing photographs - Bimota Forum - Bike performance / thrust graphs for choosing gearing

[Phil_P]

Making your engine run hotter by blocking off the radiator will not make an appreciable difference to carb icing unless you can manage one of two things

1) You can transmit enough waste heat to the carb body to prevent ice from forming. Unfortunately, most bike makers go to a lot of trouble to insulate their carbs from engine heat to prevent fuel evaporation problems.

2) You can warm the inlet charge (in this case the air) to a point where the drop in temperature still allows the charge temp to remain above dew point. Again, unfortunately, most makers take their inlet air from a point that isn't affected by engine temp, as a colder charge means denser air means more power.

Blocking off the radiator may give you some extra heat getting to the carbs, but you are forcing your bike to run hotter than design, especially if you get stuck in traffic and have reduced air flow. Boiled coolant and popped off hoses anyone?

The reason Land rovers and similar had radiator blinds, is that even with a thermostat in circuit, the engine was still being over-cooled in cold weather, it had nothing to do with carb icing (they used them on diesels too, and they don't suffer from it.

Your best bet in the absence of carb warmers is to duct some air heated by waste heat into the air box, perhaps from behind the cylinders or radiator. You can get corrugated metal hose from a car part place that will do the job nicely, then just splice it into one of the existing air pipes leading to the air box, or cut a new hole and silicone it into place.

Light aircraft which fly around in circumstances where carb icing is much more likely than on a bike, (and the effect is also potentially fatal), have a lever in the cockpit that does exactly the above. Carb heat is switched on whenever carb icing is really best avoided (like final approaches for instance).
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Moto Guzzi 1100 Sport Injection '96

[andys675]

[fenton]

My mate had a problem with carb icing on his SV. Went in and got some carb de-icer just poured a cap full in when he filled up, sorted it out straight away.
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CBR400RR NC29 ( '06 - '09 )... TL1000 RK1 ( '10 - present )

[baldy]

i used to have the same symptoms on my old sv. It was the throttle position sensor that was playing up.
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[Whosthedaddy]

Interesting read lads with some cheap fixes like the additives. I am not lying if I told you that the idea of carb icing with the 7R has scared the pants off of me when the temperatures in the morning have been getting lower and lower.

Cold and damp worst case scenario, gotcha.

What to do if the bike packs up due to it, is it just wait at the side of the road and wait for the little bits of ice to melt?
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[Bardeey]

Hi!

Could this "Carb Icing" be the problem with my bike that I witnessed last night?

Last night was the first time I have noticed it.. I was leaving a football game (It was very cold) and the bike started without any problems on the choke as normal.. I was going along fine and came to some traffic lights which were on red so as normal I keep revving lightly holding the clutch in as the bike dies unless really warmed up (Can't keep steady revs) when the lights went green I pulled the throttle and hardly had any movement, 5mph??? then all of a sudden without twisting any harder I'd be doing 20mph!!! It would just jump almost like there was a blockage and the jet had become clear.

This morning I took my carbs apart to check for dirt etc and see if there was any blocking however they were all spotless.

Could this be carb icing?

Ta

Suzuki Bandit 400 GSF
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[Kickstart]

Hi

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