I decided to get my Honda XL out to prepare it for riding the next couple days. took it outside and played around , bam , it froze also in about 3 -4 minutes, which would be 1/2mile to 1 mile, same as the XT's. So this got me scratching, and wondering,so I dug out my 2008 KTM XC525 , it has an fcr carb, 4 minutes later I was pushing it also(I stayed around the house so I wouldn't have to push long). I seems no carburated small engine can run in the current 93% humidity and 25F. I don't think it has ever been so humid yet below freezing, this just sucks, no riding for a week or so , forcast continue to show high humidity till next week at least.

I decided to post an update on this. All winter I continued to have freezing issues with the 2 XT's that I ran the rest of the winter, the others got parked. Any time the temps got up to 24F roughly and above ,I had to really watch out. I ended up putting a thumb warmer pad to the side of the left carb right under the choke, plus a copper tube with one hand warmer wrapped around it so it heated the air as it went into that carb( how much it did I can't tell). I rode that one 90% of the time , down to -19F, no issues when really cold. The heaters seemed to help but I was only running shorter distances so it was hard to tell for sure.

Today it got up to 43F(65-70%humidity) finally so I had to run an errand about 20 miles one way. Took the bike and even with the heaters on high, it still froze up. I could keep it running if I kept the throttle so the needle was opening the main circuit but if it dropped down it died. When the pilot circuit freezes up it won't start again so, I had to sit for 15 minutes, i left the heater on for most of that time, and it fired back up and ran normal. As I got near home again it was sputtering and I knew it would die again if it dropped to the pilot circuit. Made it home and it immediately died once I let it idle . A different carb setup is going right to the front of my list, I hope to ditch these carbs in all of them now since they make them only warm weather bikes. I must have ridden my klr and XL more than I thought in the colder times to not have this issue so bad before , there were times that one would die and eventually restart, so that must have been what was going on just didn't know about the freezing ,even when warm.

Never had that problem with my carb, i have been mostly riding at about 13F-25F, have about same humidity.

If it was only one bike that is doing it I'd be looking mostly at it. The fact that all had frozen up earlier, and the 2 I ran all winter doing the same, I'm out of options as to what can be going on. getting gas from 4 different stations, adding "heet" to the gas , heaters on the carb , letting them run till fully warmed up inside the heated garage, wrapped motor so the carbs are surrounded by the heat from the head/cylinder, and on and on. Once that real high humidity went away, the XL and my quads had no issues. I know exactly where they freeze up, the small passage that runs along the left side of the left carb and turn 90 degrees down to the pilot jet and connects to the choke passage, it shuts the siphoning effect off so gas can't be drawn up to the jet and since it also blocks the choke system, adding choke does nothing . Once frozen and given time to melt, they tend to be hard to restart because of the water from the ice being sucked in, but a few more kicks or seconds of the starter they pop off and stumble to life then clear up.

Up to 24-25F I had no issues either, it's that area between 25'ish to 35F (or I thought that was the high till today) that they freeze up.

Maybe its a problem that you come from warm garage and out in cold, i have mine in a garage that is no heat but keeps temp a little higher than outside. You have 3tb carb on or the old? would try the 3tb carb.

I know it isn't from the heated garage going out because once it was cleared up yesterday(was outside for an hour and a half already), it wouldn't have frozen again on the way home. It was only 12-14F colder outside to begin with anyways so everything was evened out long before it even froze up.
I only have the older versions of these carb ,'89 and older , none that came from a 3tb. The only ones I've seen for sale have been $200 +, no way I'm buying a set of these carbs for close to that.

This spring till the snow was gone I couldn't ride much other than the Honda. Tried numerous times and unless I was only going 1 mile or so I usually could make it , usually. Several times I had to keep the rpms up (3500-4000) so on the second carb, then I could make it home, but it would shut down as soon as I let up on the throttle. Once the snow was gone, I hadn't had any issues, but till then had it freeze up @ 55F once.

That was 3 weeks, and no snow on the ground=no freezing. Last night we got 3-4inches of snow but was 42F by noon, didn't make it 1/2 mile and she froze up and died. Pushed in to work and put inside for 1/2hour with my heater on, by the time I left the left carb was hot to the touch. Made it four blocks and she froze up. Never, ever, ever, have I even heard of such issues with carbs freezing so bad. Basically the only way to end it is to pre heat the incoming air to 500F or dehumidify all the air before it gets to the carb if I want to ride in the winter or spring.

I'm going to have to deal with a crumby Raptor carb intake cobbled up mess just to end this by the next winter or redesign the frames for more carb options without pods. If only I didn't dislike Honda's so bad I'd just switch.

It is far more problematic when you are up in the air in a small plane. Problem is more likely at part throttle opening, especially idling. Small planes solve it by a lever that directs intake air from around the cylinder heads instead of direct and putting up with the loss of performance - which after all is a lot better than having no performance.

Icing chart here

http://www.casa.gov.au/wcmswr/_asset...cing_chart.pdf

When it happens for real the whole air intake passage ends up almost solid ice so I'm not sure drilling out a pilot passage by a thou or two is going to make much difference. In a plane, if the engine stops due to icing (because the pilot has ignored the signs), you have seconds to select carby heat otherwise the engine cools down and there is no heat to melt the ice.

__________________
Tony
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I can sympathise with all of that. I have an old car that does exactly the same in more or less identical conditions and has spluttered to a halt with the carbs iced solid on many occasions. No matter what fixes I've tried nothing seems to stop it completely.

I also have a 70's Suzuki 125 that has the carb enclosed in a kind of shroud and while initially I thought it was for cosmetic reasons, running the bike in the winter without the covers does give carb icing symptoms. I'm so used to them from the car I can tell pretty much instantly what's happening. Putting the covers back on so cylinder heat is blown backwards over the carb fixes it and I've run it for thousands of miles without a problem.

Sadly doing something like that is not an option for the car because of the engine layout. Over the years I've tried various chemical additives, running a lightbulb in the airbox, wrapping the carbs in electrical heating cable and various lashups to blow exhaust heat over the carbs. None of it has really worked. It must just be something peculiar to the carb design as I've other bikes that don't suffer from it at all.

Tony, I had looked into airplane deicing and one place had a good explanation of what cause it and where in a system it will. They showed a 90 degree corner in a passage causes a low pressure zone on the inside of the corner where ice builds up, the sharper the corner, the worse it'll ice up.

When looking at these carbs, there is a sharp 90 degree corner right above the bowl where it then goes down to the pilot jet, so worst case, that's where it freezes and I have a thumb warmer pad right above it, only place flat enough for it to make good contact, so heat is right there but does no good, plus cardboard trapping head/cylinder heat in around the carb, so by design, it's screwed under high humidity and cold air(snow must add to the chill despite air temps). The only other thing I was thinking of is drilling the port out from the side and running a tube outside and back to the intake bell using a big radius to get rid of the square 90 deg corner.

My hybrid bike at least is allowing me to drop the motor down so it'll have room for Raptor carbs or the efi setup the won't fit in the stock bike, so maybe I'll be able to just shove this bike in the corner for the winter/spring and ride that one.