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Carb overflow peeing out fuel - stops when petcock set to RES


lowside
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Hi all,

I'm hoping someone can give me an idea of what the problem might be.  Bike is a 2022 Sherco 250 Fajardo.  Carb is Keihin.  I bought it about a month ago as a good used example.  I rode it for an hour, then stored it for around 4 weeks.  No issues.

Took it out today for a couple of hours.  No mishaps, falls or anything unusual.  Not sure if any leaks, but didn't notice any smell.  Bike ran fine and I'm just a beginner, so it was just gentle riding around, mostly watching my son ride.

Drove it home once cooled and put it in the garage.  Realised whilst browsing manual for something else, that the petcock position i thought was off, is actually reserve according to the manual.  To prevent possible leaks, I went out and moved it to what the manual calls the off position.  An hour later I'm in the garage again and theres a strong smell of petrol.  Looked and the entire garage floor is flooded with fuel.  Almost whole tank has drained.

Further inspection shows that the fuel was coming from the carb overflow and it wasn't dripping, it was gushing out.  However, fuel only comes out if the petcock is set to what the manual calls the "on" or "off" position.  When in the "reserve" position, it doesn't leak at all!  To be honest, I think I'd stored it for weeks with it in the reserve position too, having got it wrong from the start.  I'd periodically checked for leaks and there had been nothing, so I'd convinced myself I'd got the correct position.

I've been reading around and I can understand how certain issues with the carb that would cause it to overflow, but that doesn't explain how the tap position is affecting this so absolutely.

If it was an issue with the float valve, surely it would happen in all positions that allow fuel, so, reserve and on.  However, as explained previously, the leak only stops when the tap is in the reserve position!  Fuel tap looks original to the bike, as far as I can tell.

If anyone can offer any insight as to how this might be happening, it would be a great help!

Thank you!

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Just to update my original post.  It seems that the Sherco manual is wrong and that what is documented as RES, is actually OFF.  I've tentatively confirmed this by looking at multiple photo's from different dealers of used bikes for sale and all of them show the petcock in what the manual calls "RES".  I can't imagine all these dealers failing to shut the fuel off, so I must therefore conclude the manual is incorrect, or I'm reading the wrong manual, but it's the right year and model.

It adds up, given the symptoms I've got.  Still, it does seem there is an issue with the float valve, so I'll have to speak to the selling dealer.

If anyone reading this has any advice, I'd be glad to hear it.  I don't have much experience in this to be able to fight my corner.

Thanks again for reading.

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9 hours ago, lowside said:

Just to update my original post.  It seems that the Sherco manual is wrong and that what is documented as RES, is actually OFF.  I've tentatively confirmed this by looking at multiple photo's from different dealers of used bikes for sale and all of them show the petcock in what the manual calls "RES".  I can't imagine all these dealers failing to shut the fuel off, so I must therefore conclude the manual is incorrect, or I'm reading the wrong manual, but it's the right year and model.

It adds up, given the symptoms I've got.  Still, it does seem there is an issue with the float valve, so I'll have to speak to the selling dealer.

If anyone reading this has any advice, I'd be glad to hear it.  I don't have much experience in this to be able to fight my corner.

Thanks again for reading.

It is fairly common for premix fuel to form a gum on the surfaces it is in contact with, if the bike is left with fuel in the float bowl between rides. 4 weeks is long enough for this to happen. If you are going to leave the bike for more than a few days between rides, it is prudent to run the float bowl to empty at the end of your riding session or to drain it after your riding session.

The main two places where this gum tends to cause problems are at the float needle valve and inside the pilot jet orifice.

Your problem may be from this, or it could be one of a few other causes for a float needle valve not sealing off properly. To diagnose the cause of the problem, the carby will need to be taken off the bike and the float bowl taken off to allow internal inspection.

It's good that you have learned that owners manuals are to be treated with suspicion.

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1 hour ago, feetupfun said:

It is fairly common for premix fuel to form a gum on the surfaces it is in contact with, if the bike is left with fuel in the float bowl between rides. 4 weeks is long enough for this to happen. If you are going to leave the bike for more than a few days between rides, it is prudent to run the float bowl to empty at the end of your riding session or to drain it after your riding session.

The main two places where this gum tends to cause problems are at the float needle valve and inside the pilot jet orifice.

Your problem may be from this, or it could be one of a few other causes for a float needle valve not sealing off properly. To diagnose the cause of the problem, the carby will need to be taken off the bike and the float bowl taken off to allow internal inspection.

It's good that you have learned that owners manuals are to be treated with suspicion.

Thank you for your advice.

I had emptied the float bowl fully on the previous ride by idling, but yesterday, I ran it down but probably not fully empty.  I think I didn't quite turn the fuel tap far enough towards off, as I've now found it had a very slow drip on the way home. 

The carb shouldn't leak like that anyway from what I can gather.  My understanding so far, is that the carb float functions in a similar way to a british toilet cistern, in that the float should cut off the fuel if the level gets excessive?  With that in mind, it seems like the basic problem (other than an incorrect manual) is that the float needle is either damaged, or being impeded, or theres crud in the float chamber of the carb.  The bike is only a year old, so my money has to be on muck as you suggest.

As cleaning carbs seems to be a routine maintenance task, rather than run it back to the dealers, I think I'll spend some time familiarising myself with its removal and cleaning.  I can't keep taking it back to a dealers forever and I'm sure it wont be anything too complicated this time around.  Whilst I'm at it I think I'll fit an inline filter too.  I just wonder if the dealer cleaned the carb before they sold the bike.  As it's also been stalling at idle periodically, I reckon what you said is entirely accurate.

A learning opportunity for me, and I'm grateful for you folks who take time to help out in situations like this.

Edit:  For anyone looking at this in years to come, the carb on the Sherco 250 Fajardo 2022 model is a Keihin PWK 28.

Edited by lowside
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First time stripping a Keihin needs care when removing and refitting the float bowl.    The description below comes from Splatshop's website.

Remove the float bowl, turn the carburettor upside down, remove the 2 securing screws and then gently pick the float bowl up from the back right hand side first (as you are looking down at the carb in the upside down position). You need to lift this corner up by about 5mm with the carb upside down, then the float bowl should gently come right off, be warned it isn’t easy till you’ve got the hang of it and don’t force it as you will bend the floats or the overflow pipe.

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21 minutes ago, arthritic said:

First time stripping a Keihin needs care when removing and refitting the float bowl.    The description below comes from Splatshop's website.

Remove the float bowl, turn the carburettor upside down, remove the 2 securing screws and then gently pick the float bowl up from the back right hand side first (as you are looking down at the carb in the upside down position). You need to lift this corner up by about 5mm with the carb upside down, then the float bowl should gently come right off, be warned it isn’t easy till you’ve got the hang of it and don’t force it as you will bend the floats or the overflow pipe.

Right, thank you for this.  I will keep in mind when I do the job.  Parts for the carb are quite expensive, a new float valve is £7 on its own!

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