Fatal carb flaw
 

This last week and a half all 4 of my runable(aka titled and together) XT's refuse to run more than a mile before the carbs freeze up. It is one of the air passages not the gas (half the time it actually 1 or 6 degrees above freezing. I can have one die, push it home or sit for fifteen minutes if the motor was warmed up and sometimes it'll start and go for 1/2mile then quit. When I get home I start up one of the others, running perfect go 1/2 to 1 mile then die.:stormy: Put them back in the heated garage and fifteen to 30 minutes they'll fire right up and run till out of gas, but go outside and 1/2 mile -puke.

Tried it with all of them (stuck close to home so not far of push), everyone did the same thing. I ran all winter last year, even down to -15F, never had a freezing issue, even ran them earlier this fall at -6F. Humidity is 85% to 98% for some dang reason and I can't ride any of them even though roads are basically clear and temps are 26F to 38F until the humidity goes away. It is pissing me off ,even enclosing them with the head/cylinder with a wrap of cardboard to help warm the carbs didn't work. This is unbelievable !:censored: I sold my other brand bike so nothing but XT's and an XL which I don't really care for, but it'll run.

This is interesting, let us know when you figure it out, I know you will....

Not much to figure out I guess , these specific conditions are just unrunable with these particular carbs. Same temps but with normal humidity and there won't be any problems, same goes for the high humidity with either warmer(my guess is 40-45F or less than 20F(I had no problems the other morning @ 15F). To have 95% humidity and below freezing here is almost unheard of , it should be freeing out ,but for some reason it won't. Just getting me ticked how bad they kill the motor so fast. Of all the toys I have owned , never, ever seen this kind of air freezing inside the carb.

Do a carb swap. In the winter of 2012-2013 I've tried some ice riding on my XT. Couldn't do more than 10minutes (after 2km ride one way to the lake). The carb would frost up. NOTHING helped. Fuel additives, etc...

After I've finished a Raptor 660 carb swap, in the winter of 2013-2014 I was riding happily with NO carb frosting what so ever.

Edit: both winters I was riding the temperature was as cold as -25 Celsius. And the humidity was high around the bike's intake, as snow was coming off the front wheel on the exhaust, melting, and the steam was picked up by the intake.

We got XBR's to run longer by heating the air inlet. First of all using a deflector off the cylinder and tin foil, then copper pipe wrapped round the exhaust header. The ultimate would be an elecrical element like the old propellor airliners had but we never got that far.

Andy

As far as I know at least some KTMs are using electrical heating in their carbs...

If the humidity goes away ,so will the freezing, I'd like to have a backup just in case for the bikes that I am keeping these carbs on. The others will have efi (working with Yoshimira on a retrofit setup). I think any electrical or coolant(snowmobiles) heating setups require a carb change and I do have some Raptor carbs I could install if I wanted to go that route. I will not run pods so until I find a way to keep an airbox with them I'll be running the stock setup.

The one thing I need to find out is if the freezing is from the way the air is being introduced or if the little passageways are simply too small for these conditions. I'm 99% sure it is the tiny little intake hole on the left side that feeds the pilot circuit and mixture screw causing all the issues,
http://imagizer.imageshack.us/v2/640...537/7SDMaN.jpg

Connect heat element on that side and you will know.

You have "carb icing" and a fuel additive will fix it. I don't know what it is called now, but Silkolene FST (Fuel System Treatment) was the one I used.

It works. 100%.

It isn't the fuel that's freezing, it is the air passages frosting up. It's has to do with the effect of air being squeezed down through a small opening, my compressor fittings ice up when I use my sandblaster if there is moisture in the air, same thing. I had already added some de-icer to make sure.

Actually it is just the opposite. When the fuel/air exit the squeezed down area in the carb, the venturi, the expanding area's air pressure is lowered and temp is lowered. Just like an air conditioner, once the freon passes the orfice and pressure is released, the freon gas gets very cold in the evaporator. It is the high humidity that is freezing, I think external heat may be the best solution. Back in 1971 I was driving a Toyota Celica here in the USA that I had purchased while on the island of Guam. It did not have a heater or a preheater for the air filter as the USA models had. I had freeze up problems all the time in high humidity times. Only way to get going was to wait until engine heat melted the carb throats. My eventual solution was taking the car back to Guam on the next tour and sell it there....

That's what I was saying, the air going through the passage is speeding up do to the restriction, but isn't being compressed(which would heat it up,aka- turbo), acts the same as air going from being compressed to releasing of the pressure, it cools down and freezes the moisture, in this case it is still in the passage when it freezes. Sounds like tomorrow the humidity is going to start dropping so I can start riding the XT's again. I did run the XL without issues. Was able to take the down time to convert a bunch of bulbs to LED. Still waiting on the headlight to see if they're worth it.

I can also say no fuel additives helped me either. Myth busted.

Old VW Golfs with the Pierburg 2E2 Carbs used to have a tiny heating element encased in rubber to stop this problem(it didn't)
You could try and find one of them and fit it to the carb to stop this happening.
I am sure they are not the only manufacturer to have tried this on Carbs for cars.
I know that in some markets the Honda NX650 had carb heaters installed to prevent this occuring.
It should be easy enough to find a small heater and fix it where the problem is with a small bit of steel and a 12v feed.

I found some little elements from KTM for it that plugs into the electrical system I'm going to try. I attempted to make it to work this morning with one of the other bikes but didn't. I made it to the gas station I know and they put it in there heated garage . On my first break (3hrs later) I got a ride down there and thought I could make it 3 blocks to my work. It fired right up on the first kick, let it idle for a bit inside yet, took off and made it one block before it started stumbling, then quit. 100yrds !!! :censored:
Humidity is still quite high , hopefully tomorrow it will be colder and drier. I can't keep this up all winter and I refuse to park them !!!:stupid:

I am going to drill that orifice out another .01" maybe and see how it effects fuel mixture, I assume it will probably need to be jetted a lot leaner. The bigger hole will take more to get blocked off.

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.

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.