Hi do you think that my exhaust on my 2011 sherco 290 could be causing my bike to die after 4 hours of riding and causing the spark plug to go like this. I am getting the exhaust cut open and repacked to see if it stops the gasping noise the bike is also making when i rev it. The spark plug isn't oily and the bike mixture isn't to rich. Any advice would be appreciated many thanks Dw   

Edited November 27, 20169 yr by dwb5151

Check the air going in and the fumes going out. What is the condition of the air cleaner?

I started the bike a while ago black liquid came out of where the spark plug goes. The spark plug wasn't in fully tight as i was just starting the bike to see if the fan was running. I took the spark plug out and smoke came out of where the spark plug goes. Every so often when riding the bike i would have to rev it hard to get it to rev properly giving me the idea that the exhaust is what is causing the spark plug to go like that. Some times smoke doesnt seem to come out of the exhaust then sometimes it would.

Try a new spark plug before you go any further.

A mate of mine inadvertently put a bit of DERV in with his petrol/oil mix with similar results.....

I have tried 3 spark plugs all of which are being sooted after 3 to 4 hours of riding. I am going to get a fuel filter for it just make sure no dirt get in. The bike also had blocked jet as a result of dirt in the fuel pump. Which was cleaned.

Check the air filter.

And drain the fuel completely, tank and float bowl.... refill with fresh fuel with the right fuel oil mix and try again.

 You all forget, he has a bike with a vacuum fuel pump. Lot`s of other issues here.

Ah, I see. It suffers from progress.......

Some time back, over two years ago, I had a 1999 Sherco and had the same problem, it just started doing it, id had the bike for around six months and the plug was fine but then it started to bog down and the plug would look the same as yours after just a few hours, the only thing I had recently done to the bike was change the oil but I used a different kind oil than I normally used, I changed the oil back to the oil I normally used and it solved the problem. I don't know what was going on with the other oil, I'm certainly no mechanic but it sorted my problem out and the bike ran fine after the oil change. 

Some time back, over two years ago, I had a 1999 Sherco and had the same problem, it just started doing it, id had the bike for around six months and the plug was fine but then it started to bog down and the plug would look the same as yours after just a few hours, the only thing I had recently done to the bike was change the oil but I used a different kind oil than I normally used, I changed the oil back to the oil I normally used and it solved the problem. I don't know what was going on with the other oil, I'm certainly no mechanic but it sorted my problem out and the bike ran fine after the oil change. 

Funny you say that i changed to a different 2 stroke oil putonlon one which i used on my older bikes but not on this one

What makes you so sure the bike is not running rich?

What makes you so sure the bike is not running rich?

The spark plug isn't oily. There's a weird smell coming from it . I took the exhaust off and i notice the spark plug smells exactly like what the exhaust does inside. That made me think that the exhaust fumes aren't getting out creating a back-flow causing all the exhaust fumes and oil going to the top head causing the spark plug to go like that. As i noticed when riding some times it wouldn't rev properly and i would give it a hard rev and then smoke would then come out of the exhaust. 

Did you check the fuel pump diaphragm for wear/holes, has fuel lines and vent been updated to new much improved way...proper routing and no blockages in hoses...