Hi all, I have recently purchased a new 2010 250 and have been out a couple of times since. I have noticed what sounds like a 'clunk' or 'knock' when the engine is revved under load, say when climbing a hill.

At low revs it seems ok. I've done the usual like check the mixture screw and made sure the flow from the tank is ok.

Would appreciate your thoughts on this.

Cheers

I know it sounds daft, but are you using high octane unleaded (like vmax). Makes hell of a difference from regular unleaded. Just a thought. I thought mine was on the way out, when I had a can full of it.

I think what you are referring to is normally called pinging(or pinking) yet can indeeed vary in intensity into a knock.

In many ways, this is somewhat normal for Sherco's and some other bikes as well, as they are all a bit "on the edge" as far as tuning goes.

To run pump gas(yes they will) it's gotta be the good stuff! 98 RON.

Carby jetting and tuning also come into play, and this can get into quite a bit of experimentation and time consuming.

In what you describe, you are at say mid throttle with fair to heavy load on motor pulling a hill, you are in the needle/ main jet operation range and you might try raising the needle(dropping the clip) a notch or even two just to ck results and changes. See where you get with fuel first.

None of this is necessarily damaging on just a short period hillclimb.

Another example would be my '07 bike, which would ping on a lighter load, example crusing down a road or trail in 4-5 gear at 30 or so mph and 1/8-1/4 throttle.

I never lost the pinging till I went with the 38 pilot jet, as on a dellorto it is still in the game at that time, mind that is on US fuel,(crap)!

Hope that helps,

Check the pilot jet size, it might have a 30 in it, if so swop it for a 33.

Get a inline fuel filter fitted before the fuel pump, were the fuel exits the tank down by the chain, it's probably worth cleaning the fuel pump too as any little bits left over from manufacturing the tank will slowly get sucked up into the pump stopping it working properly, this will lead to lean running and knocking/pinking noises.

One last thing check the breather pipe for the tank isn't sticking out of the bottom of the bike, if it is it can get blocked with mud which will make your bike run really rough. I cut mine off at a 45 degree angle and make it quite a bit shorter so it's out of the way of any mud. Also check the pipe isn't kinked under the rear mudguard.

Hope this helps.

Cheers lads, that's great.

I'm using super unleaded which i think is 98 RON. I've done the fuel line mod but will recheck it and will also clean the pump out.

I'm not sure what the pilot jet size is but the 33 sounds like a good option.

I'll keep you posted as to the outcome. Watch this space as they say.

Many thanks

Ok gents, an update on the above.

I've fitted the inline filter and shortened the tank breather at the same time.

I've removed the carb and the pilot is already a 33, there was another jet that had 122 on it, is this the main jet?

I attempted to drop the clip on the needle as Copemech suggested but I couldn't see how to do this, any suggestions?

Also I was thinking if the timing was slightly out could this cause the problem?

Cheers

we run all our bikes on full syn ipone samurai and ordinery unleaded at 100cc oil to 5ltr petrol and never had a problem.

Ok gents, an update on the above.

I've fitted the inline filter and shortened the tank breather at the same time.

I've removed the carb and the pilot is already a 33, there was another jet that had 122 on it, is this the main jet?

I attempted to drop the clip on the needle as Copemech suggested but I couldn't see how to do this, any suggestions?

Also I was thinking if the timing was slightly out could this cause the problem?

Cheers

I would doubt the timing is off, personally, I would make the change to a 36 pilot jet and ck the results. You will need to bring fuel screw in a bit(maybe a turn) to achieve best running. Main jet should be ok i would think. Mind, this is soo difficult to tell due to fuel variences. What you get there is just different it seems, yet others there seem to have had good results based upon general feedback.

At least you have a good idea where you are at on the jets. Write it down!