sherco 250cc 2011 ,

Ive been told my bike is " hunting" after twisting the throttle the revs stay high and slowly build down, when iddling the revs build up or sometimes slow down till it stales

Ive cleaned the carb myself and had it done by a local bike shop ( not a trails bike shop)

Second time i took it back they replaced the crank seal,

I still have the same problem!

Im not very mechanicaly minded with trails bikes and am wondering what to try next as im at my wits end now, any help would be much appriciated, thanks,

Hi there i have a 2011 sherco 250, the problem you are having could be an air leak between the crankcase manifold and the carb try that, to find an air leak spray brake cleaner on the manifold then you will know.

You say they have changed crank seal could it be the other seal thats gone,you can also use wd40 to spray on inlet manifold to check for leak ,does sound like bike is sucking air from somewhere.

Good luck.

Hi

clearly your on the right track. Revs taking time / not settling down is weak running.

A suggestion list:-

• Crank seal (done?)
  
• blocked idle jet (done?)
  
• air leak at crankcase halves (rare if the engine hasnt been splt recently)
  
• Air leak at reed valve manifold (either side of the manifold)
  
• Carb not seated well into intake rubber
  

The most likely is the crank seal on the flywheel side (repaired already?). Common on Sherco's, this can happen on the clutch side also, but normaly is accompanied by smoke from burning gearbox oil.

Blocked pilot jet or poorly adjusted idle screw (repaired already?). These can lead too poor starting / slow to return back to idle but the difference with your symptoms is the revving up without touching the throttle... this says air leak.

A rare occurence is leaking crankcase halves (happened once to me). Usually caused by poorly fitted crankcase gasket during rebuild. Can sometimes be caused by a cracked crankcase due to an impact.

So the list isnt too long, a couple of hours should see you in the know.

Dom

Hi, As the other guys have said, It sounds like its running weak. Fuel starvation can also cause your symptoms, Check the fuel tank breather tube and the 1 way valve in the tube isn't blocked also check the fuel filter, fuel tank & fuel pump also.

mine did the same. Solution was to buy a beta !

The problem on mine was the pilot jet. They are so small they block very easily. I had to fit TWO filters before the carb to get it anywhere decent. And even then is was a temperamental SOB. If you are running the same dellorto carb, I'd bet it's your problem.

My advice would be to ditch the carb and fit a kehin if you can afford it.

Even water droplets in your fuel bowl may cause this! Untill you know your CAN, TANK, CARB are totally clean, including pilot jet, you are peeing into the wind!

My dads 1998 270 Gas Gas does this only when cold but once the cases heat up its stops.

Must have an air leak somewhere but then the cases expand at the joint in the middle sealing it . when warm

Hi I recently had a similar issue. Purchased an 05 290 after it just had a total engine rebuild. The bike was taking ages to start. Usually tireing me out and then have to give to someone else to try. Once started it would take ages for revs to die down. Done a training course on it and was fighting constantly to keep it slow. Got home and removed flywheel, retarded the ignition. Now she starts second kick and is lovely to ride.

I spent 2 years finding a hunting problem on my 250 Sherco so I might know a thing or two

Unless it's on the inlet manifold I doubt that you have an airleak.

Five questions...

Has it every been Ok?... if so when?

Does it get worse when it's hot?

Have you changed your fuel, fuel mix or altitude more recently?

What Fuel Octane and 2T Oil are you running?

What Carb are you running?

All the best.

Neo

Good evening all,

I am experiencing a very similar issue and wondering if dixon ever sorted it out?

I don't experience the climbing revs on its own but do get the idle hunting and occasionally have to use the clutch/brake to return the engine from revving high when HOT e.g. Climbing a hill the ease off the throttle at the top, but the engine continues to rev high which does not end well for me :-)

I am competent in mechanics and have replaced all seals, fuel filters/ lines, inlet seals both sides, cleaned tank. But still get the issue, I don't know the history of the bike but looking to understand what to try next before ripping the engine apart....

Things I've NOT done that I'm suspicious about are reeds (seemed ok?) carb setup (not a expert) but would mixture etc cause such issues like this?

Also hear people retarding the ignition on these bikes?

What would you kindly suggest I focus my attention to next?

Many thanks in advance.

Paul

Hi Paul,

I did all the same things as you plus a whole lot more .....with 3 different carbs too.

I can give no guarantees but have a go at using low octane fuel with a fully synthetic 2T oil (Like Castrol 2T Racing) then adjust the fuel mix (Dellorto) or air mix to run sweet when warmed up. Depending on past setup you may also need to go for a larger pilot jet too.

If the reeds were buggered your problem would be consistent .... And my guess is your having good days and bad days? .... Depending on the air pressure and humidity etc....

Best of luck.

Neo

Soo, if I understand all that correctly you replaced the crankshaft seals and have not gone through the carb?

Neo - thanks I will baseline the carb then play around with the mixture to check the outcome. I'm running 95 RON and did think about the octane, raising/lowering.

Copemech - sorry just re read my post think I missed the crucial word :-) "all carb seals are done".

So I have not done crankshaft yet, I'm try the cost/time effective process of elimination first. I can ensure that the carb is clean and air tight, also the inlet and reed housing.

The only element of the carb I have not completed is the mixture setup.

In my experience 95 is too high.....get 91, if you can, then tune from there.