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.