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Discussion Starter · #1 ·
2002 FXST Carbed 2,700 miles on the clock.
Outside temperatures ranging between 2 and 8 centigrade.
The bike seems to run well if anything a bit slow in getting to the point of idling unaided (i.e. choke or throttle input).
Then it goes through periods of running very rough, misfiring, backfiring and basically I struggle to even keep the engine running.
If I then give it a whopping (go through the gears to the limiter) it seems to be running better for a while and then the same thing happens.
Oil temperature doesn’t get over 150 F. and I do not remember having this problem when outside temperature was higher and oil temp would get to 200 F and over.

Could it be that the bike is running too rich and does not get to the right operating temp when the outside temp is below 10 C? This would probably foul the plugs and compound the problem, right?

Could anyone shed some light because I am worried that there might be something big goin’ on (valves, rings, god knows what else)?

Thanks for your help.
 

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Cold Rider said:
Your carb is icing
Does an icing carb indicate a slight amount of water in the fuel or does the water come from condensation inside the carb itself? Thanks.
 

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94c4:

What's the setup on your bike, ie, air cleaner type, pipes and carb mods?? I hear more about this condition on stock carbed bikes due to their lean condition in the low speed range and also in the transition from low speed jet to needle. Could also be caused by an intake or exhaust leak.

I don't know all the engineering terms, but no, it is not caused by water in the gas. It's a condition caused by outside air temps plus humidity and subsequent air flow into the throat of the carb.
 

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Discussion Starter · #5 ·
Thanks y'all.
Ed Y. Bike is running SEII mufflers with SE airbox and rejet kit.

Whether in london IS cold and humid! Hell, we have a bloody river running through town!
:D
 

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If you don't have an exhaust or intake leak, don't really know what else to tell you. I have heard of some guys in cold country here that put the stock air box back on for the winter but that's kind of a pain. Also had a couple of friends that put a Turbulator in the throat of the manifold and solved their problem. But, we don't get that much cold and humid in south Mississippi. I rode to Daytona last spring in temps ranging from 32 to 40 for about 10 hours and didn't have any problems with my 99. I've just got free flowing muffs, air cleaner and sporty needle in the carb.
 

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Discussion Starter · #7 ·
Cheers Ed!
Can't figure it out.
Rode back from work tonight (possibly a couple of degrees warmer than this morning) and everything was fine. Oil temp did get up to 170.
It's got to have something to do with temperature.
Is there any way of getting the engine to run hotter?
 

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94c4 said:
Cheers Ed!
Can't figure it out.
Rode back from work tonight (possibly a couple of degrees warmer than this morning) and everything was fine. Oil temp did get up to 170.
It's got to have something to do with temperature.
Is there any way of getting the engine to run hotter?
I assume you are taking oil temp from a gauge on the dipstick? You gotta remember that the oil in the engine is probably 10-15% hotter than what you read at the oil tank. I think you just hit a condition of temp and humidity that caused the icing problem. I personally wouldn't worry about it. It might not happen again for days or weeks but then could tomorrow. The TC88 runs hot enough as is. Leave that part alone.
 

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Discussion Starter · #9 ·
okay thanks, I'll keep my fingers crossed and my hand on the throttle.

What is icing by the way and how does it happen?

Ciao
 

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Just remembered that HD sells some stuff called "Winter Conditioning" or something similiar that is supposed to help with icing. Here is an explanation I saved from another forum some time ago. Written by an airplane guru. Prop planes deal with it all the time. It's lengthly but what the he**.
..........................................................................................

You cannot have carburetor ice below 32º F because there is no
moisture (relative humidity) in the air. Any moisture in the air at
32ºF and below is in a solid (ice) form as sleet or snow.

There are 3 types of icing.
1. Fuel vaporization ice: This is the most common and occurs
when fuel changes state from a liquid to a gas. It is common to a
temperature drop of up to 70ºF as fuel robs the temperature of the
induction air to change state. Fuel vaporization ice can occur at
ambient temperatures as high as 100ºF and humidity as low as 50
percent. It is more likely, however, with temperatures below 70ºF and
relative humidity above 80 percent. The likelihood of icing increases
as the temperature decreases down to 32ºF and as relative humidity
increases.
2. Impact Ice: This is where snow or sleet freezes to you air
filter element and causes blockage of the induction air to the
carburetor.
3. Throttle Ice: Is formed on the rear side of the throttle
valve when the throttle valve is partially closed. This rush of air
around the throttle valve forms a low-pressure area and has a cooling
effect on the fuel-air mixture. Moisture freezes in the low-pressure
side (back side) of the throttle valve. This ice can accumulate and
restrict the income fuel-air mixture and cause an engine power loss
by loss of manifold pressure. Throttle ice seldom occurs above 38ºF.
..................................................................................
 

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Not saying your carb iced up but a carb can ice at temps above freezing. has to do with the properties of the evaporation of the fuel combined with air flow. when any medium evaporates(essentially its boiling or changing states) it gives up heat. ever drained an air tank for moisture and watched the drain valve get coated with ice? same for gas with air flowing over it. it evaporates quickly enough and when combined with humidity and air flow it can freeze. one of them principles of refrigeration, I think its called "latent heat of vaporization".
 

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yo london dude buy the winter fuel treatment from HD , I have the same problem this time of year, and yes it is carb ice , also try running the higher octain[super] from BP in the winter seems to help, merry xmas, see you on the road!
 

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Discussion Starter · #14 ·
Phantom,

I did buy that fuel additive.
As you know the weather, at least in the South, has been incredibly mild in the last ten days or so.
Therefore I have no way of tellin' whether that thing works or not.
I use BP fuel (you know, Nectar points!).

Whereabout in Great Britain are you based.

See you 'round
 

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Not sure I agree that there is zero moisture in the air below 32 degrees, but interesting read anyhow. Actually, I'm quite sure that I don't agree that there is zero moisture in the air at 32 degrees. Lets see if I remember anything from my edumacation:

Relative humidity is the percentage of humidity in the air where zero is bone dry and 100% is the saturation level for air AT A GIVEN TEMPERATURE. Cold air can support less moister than warm air, but there is still moisture in the air at temperatures below freezing. This means that 100% humidity at 30 degrees is much dryer air than 100% humidity at 80 degrees.

Right now it's 19 degrees at 91% relative humidity in W. PA. That's pretty danged close to saturation. Being so close to saturation, even slight decreases in pressure (as with localized increased air velocity in a carb) or reductions in temperature (such as fuel evaporation) will cause the water vapor to condense and immediately freeze. My brother had a CJ7 Jeep that would ice like nobody's business. Never did get that sucker to run well in the winter. Hated that thing.

Chilly
 

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Discussion Starter · #16 ·
Chilly,
I think you've got a point. I'm not sure what it is but it makes a lot of sense.
:)
 

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I use to have a VW dune buggy in the 60's. Of course in making mods to the bug, I removed the heater boxes and shrowd that went around the jugs and carb. Let me tell you, I know what icing carbs are like. The ice actually formed around the outside of the carb like it was a freezer. Of course, the same was probably happening inside. Makes one wonder if there is some method you can get some of the heat coming from the cylinders to flow by the carb. Small aircraft have carb heaters for just this reason. Otherwise, when the temp and humidity is in the right range, the carb will ice up. I doubt the type of gas (petrol) you put in it will make much difference.
 
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