Hi, looking for some help or info on carb freezing, I have a 2011 sherco 290 with a dellorto phbl 26 fitted, I was out on the weekend and the throttle stuck open 3 times, it didn't do it while I was riding the bike, it did it when I gave the bike a quick rev after I had been running about on it for around 20mins, once I got it to cut out I looked at the carb and it had a coat of frost over it. I let the bike sit for 5 mins, then try to start it again and it was perfect, at this point the frost had gone from the carb, 20mins out on the bike again and the same thing all over. it was my 1st time out on the bike and was just toting around in low revs, when I gave a quick couple of revs to the bike it was out of gear and prob a higher rev than when I was riding it. the 3rd time it did it was after I washed it at the garage then brought it home a few miles on the trailer, I dryed it of at the house took it along the street came back gave I couple of revs and it did it again. the temp was around 0/-1 all day and prob had a wind chill of even lower. any help would be appreciated.

Well I know a bit about it

Your carburetor will through evaporative cooling be a few degrees cooler than the air temp

At 1 degree c there can still be substantial moisture in the air

So the carb is below 0 and the moisture in the air freezes on contact

Well below 0 it doesn't happen as the air is much drier

It's hard to stop, you cannot jet it away but you can wrap the carb and try to get engine temperature to it

Snowmobiles run coolant through the carb body, petcock to turn it on and off

Outboards have electric carb heaters

Not an easy fix

I have never had a carb freeze up on a trials bike, yet I hear it happens. LOW throttle openings create higher venturi cooling, thus more temp drop accross the opening in the carb. This temp drop can be great like 30F, and I have had carb ice on a 60F day in high humidity conditions, in an aircraft!

The ice can make them loose power, sputter and such on takeoff! Not a good feeling!

In icy conditions we tend to start the bike and get it warm(till the fan cuts in) then stop the bike. This lets the heat radiate from the engine to the carb. If you keep it running the cold air getting dragged in doesn't let this happen.

Some older Shercos (a lot older than yours) had to have a stronger slider spring in the carb as it didn't return the slider properly. Also some riders cut a bit off the spring to make the throttle lighter to turn. Perhaps yours has been done like that.

Rather than just using low revs use all the revs to keep things moving.

Edited March 27, 201313 yr by timp

On my old Montesa I made a piece of plywood to shield the side of the carb. This directed heat from the rear of the cylinder and kept the wind off it. Only had to use on occasions when the temparature allowed the carb to ice up. Didn't look very good but did the job. Others used to use duct tape.

Hi, this happened to a friend of mine on a child day turned out there was some water in the air box ! When the air box and filter were dried out it ran perfect all day in minus three degrees c.

Birra cardboard with baco-foil wrapped around it makes an easy shield just like scraggydog suggested, I used cardboard 'cos (I'm cheap) it's easier to trim and you can stuff it in place without fear of chafing (ooh!) on anything vulnerable.

Hi gwd,i had this problem a few years ago,so after trawling through all the forums came across one that suggested to use SILKOLEAN FST PRO FUEL ADDETIVE . this sorted the problem,so know in the winter months i add it to my fuel and no more carb icing.

http://www.opieoils.co.uk/p-809-silkolene-pro-fst-fuel-system-treatment-for-petrol-engines.aspx

I'd give the carb a good clean to make sure there is no water in it. I ride regularly in cold conditions and have only had frozen carb problems when there's been some water in there. It happened the other day in fact so I quickly cleared the carb and it was fine again all day.

Hi there

I have done a lot of green lane and trials over the years in all sorts of weather on all sorts of bikes,and have had this problem many times.I found for a quick fix is an old piece of inner tube with a hole in it stretched around the carb and held with some tie straps work a treat.Try it

Good luck Roger

Seconded on the FST Pro. We had it years ago on a REV50 added this stuff in and used it since with no icing.

Hi, thanks for all the helpful replies, I will order a bottle of fst pro and give it a try, also going to give the carb and air box a clean out tomorrow just to make sure there's no water in there. hope to get out this weekend and see how it goes, think the weathers still going to be cold so should be good to try some of the tips. thanks again.

Looks like the weather's going to be perfect for carb' icing conditions for the next few weeks according to the forecasts