2011 250 carb problem

[geodet]

Anyone having carburation problems with the 2011 250?

Mine ran fine when new but after a couple of outings I am having loads of problems with the pilot jet area. Tickover and low down response is awful. once on the main jet it runs beutifully. I have tried a bigger pilot jet and that helped but it still performs poorly low down. At a local Trial yesterday it seemed that all the new Shercos were having issues, including the 290s. I dont know if this is a cold weather issue or a problem with the UK set up. Anyone have any clues?

[7]

Anyone having carburation problems with the 2011 250?

Mine ran fine when new but after a couple of outings I am having loads of problems with the pilot jet area. Tickover and low down response is awful. once on the main jet it runs beutifully. I have tried a bigger pilot jet and that helped but it still performs poorly low down. At a local Trial yesterday it seemed that all the new Shercos were having issues, including the 290s. I dont know if this is a cold weather issue or a problem with the UK set up. Anyone have any clues?

[paul w]

a few years ago we used to have the same problem with KTM's in this kind of weather. Its down to "carb icing" , i have tried to google an explaination but the ones i have found are all model specific.

Some models now have electically heated elements on the carbs.

[chewy]

Its' only a theory and it's not only related to Sherco's , is it that it just wont tick over nice and smoothly, I reckon and it may be daft that the speed of the airflow crates a chill factor as it passes through the carb, when it is as cold as we have been having it blocks the jet or restricts the airway (with ICE, albeit tiny tiny tiny) thus crreating the symtoms. Last time out at the Knut there were several of us in same situation (just an observation also but guys with bikes on trailors and racks more so thanin vans for transport) having experienced this before the trick is to get the motor warm/hot and then stop it and leave it for a while for the heat in the casings to conduct back to the carb, it worked for Sherco ,Beta and Gas Gas, incidentally when I collected my bike new I was told that the revised jet size mod for UK had been done;... (I'm talking practically first batch of 250's into UK)Also for my taste and ability I retarded the timing by c.3 degrees, that transformed bottom end response immidiatly although on map 2 it's a bit flat at top end. keeo us posted on what you find.

[baldilocks]

if it is carb icing get hold of some silkolene pro FST. Its a fuel additive that stops the carb icing up. My Gas Gas was bad for icing the carb probably due to very cold water splashing into the air filter box through the drain hole. The pro FST cured it. Sherco may be more prone as the fuel line is just above the swinging arm

[slack]

Hi all, yes like baldilocks said try some silkoline FST pro,it also cured my carb from iceing up its around about

[benbeta23]

My Evo also has been suffering with carb icing quite badly, Will give the silkolene FST a go, Thanks very much!

[dan williams]

Not sure I would call it "carb icing". That term is commonly used in aircraft and is actually a problem on warm humid days when the air at altitude passing through the venturi and then expanding drops the temperature of the incoming air to the point where moisture precipitates out into the carb throat and freezes. It doesn't happen in cold dry air.

I think what might be more likely is the temperature of the fuel is so low that it isn't vaporizing properly. Jetting it richer helps some as would adding something to the fuel that increases it's volatility. In the U.S. fuel mixtures are changed for summer and winter and if you are using a summer fuel in the winter the vapor pressure might be too low to ever work properly even if you re-jet.

http://www.kellyracingfuels.com/rvp.html

Edited December 28, 2010 by Dan Williams

[copemech]

Yes, carb icing can be an issue given certain temps and humidities, yet I am suddenly stricken by the fact that the damned alcohol laced fuel is also hygroscopic and may contain a lot of moisture that could adversly effect things with the fuel itself and dropout of water in the mix.

Clean your carbs and fuel cans as well!!!

[baldilocks]

Not sure I would call it "carb icing". That term is commonly used in aircraft and is actually a problem on warm humid days when the air at altitude passing through the venturi and then expanding drops the temperature of the incoming air to the point where moisture precipitates out into the carb throat and freezes. It doesn't happen in cold dry air.

I think what might be more likely is the temperature of the fuel is so low that it isn't vaporizing properly. Jetting it richer helps some as would adding something to the fuel that increases it's volatility. In the U.S. fuel mixtures are changed for summer and winter and if you are using a summer fuel in the winter the vapor pressure might be too low to ever work properly even if you re-jet.

http://www.kellyracingfuels.com/rvp.html

We dont ever have dry air in the North East of England Dan we have very cold very damp air.

[dan williams]

We dont ever have dry air in the North East of England Dan we have very cold very damp air.

Accepted but what's being described sounds like a fuel volatility issue. "Carb icing" is something that doesn't affect starting until after the engine has been run a while and will kill the engine while running. Which is why it's so feared in aircraft and why airplane carbs have heaters built into them. Also bike carbs are behind and in close proximity to the cylinder (except the Ossa) so they have a tendancy to be self heating to some extent after the engine has run for a bit.

I never had this issue with my old Bultaco which on hot days could boil the fuel in the tank. The Beta tank, being a big heatsink, has no problem. I've often wondered why they didn't go the extra mile and use the frame for cooling to save weight. Couple of thin copper tubes down the frame rails wouldn't have heated the frame too much but spread the heat out requiring a much smaller radiator.

[baldilocks]

If you take the carb apart on cold day when its not picking up and wont tickover the galleries in the rear of the carb, which feed the pilot jet circuit are dripping with emulsified (spelling) oil. It looks like white sludge. We call this carb icing but perhaps its not the right term ?

[dan williams]

Ah, pardon the colonial. As in cake frosting. I get it now. We may be in agreement again. Separation of low volatility hydrocarbons from the fuel mixture. I thought people were actually talking about water ice. My apologies.

[copemech]

No, I doubet either Dan or Baldi here, Ice is Ice and Emulsified crap is just that, all point being, just how is it induced?

Yes, the venturi effects of a carby, specially at low openings, will cause a drop in temp specially when combined with the atomization of the fuel.

In Baldi's case, fact is by the time you strip it to witness anything, it may have melted, sort of like the Daggar of ice, no smoking gun here. Just residue.

Other thing about the alcohol in the fuel, which may be 10% here, and if I understand correctly will absorb up to half of it's own volume of water or condensation into solution, just what happens to this percentage of the mix of fuel, alcohol, oil and water as it passes through the passages and into the cold venturi? Does the water in suspension suddenly turn to an accumulation of sludge at or near the orface? Could this gel if not freeze entirely? Huh? Doubt this crap would suddenly fall out of suspension and separate.

I have been running higher concentrations of the AV fuels during the winter months, no alcohol, and no problems. Yet at the same time, that is just my experience here, in an even warmer climate.

[neo]

You guys ever considered emigrating ... It's been far too hot to ride over here lately

Hey Cope, how about distilling that alcohol and using it for other things

Best of balance.

Neo.