Looking for a bit of advice

Just done the main bearings on my 06 rev3 250, put it all back together

, started it up and it runs fine and sounds perfect. Took it out for a run and after about 10/ 15 mins it started to make a noise that sounded a bit like a top end rattle or knock then start to die then cut out but it started up again straight away and sounded perfect, then after another few mins same again but this time didn't cut out as I managed to keep it going by pulling the clutch in and catching it on the throttle. If I go and start it now it will go first kick and sound spot on, it only seems to happen after a wee while when its under load.

The only other thing I have done is change the jets to the factory ones,27.5 and 145 I think.

Any suggestions ????

Sounds like fuel starvation to me. My old sherco had a simular issue when I gave it the beans across a field. Found out that there wasn't much flow coming from the fuel tap as the internal fuel filter in the tank was blocked so worth checking that. Or even your float could be sticking not letting fuel into the carb. Just strip the carb down and make sure it all looks ok and check the fuel flow.

Cheers

Greener

fuel starvation, or water in the petrol tank. clean the carb (take all the jets out and blow through) while the carb is off remove the fuel tap and check the filter (drain the tank first!)

It is not an easy job to get the fuel tap out Do it with the carb off The fuel stack is long so you need room to get it out The nut is right hand/ left hand thread so hold the tap unscrew the nut You may find a gooy gunge on the filter I did Also check the tank breather is clear as fuel will stop flowing correctly after running a while

just thinking about this now, the knock is pre-detonation, this might be being caused by excessive heat, check your impeller is turning and that the fan is working on the thermostat. its the 15 mins thing thats got me away from fuel, thats too long really.

Think it probably is fuel to be honest,as it only really done it after I was going pretty quickly over a field,if didn't seem to be overheating or anything,I've cleaned the carb out and changed the pilot jet back to the standard one tonight and it seems to be running good,will take it out tomorrow and try it

Cheers.

Mate just take the fuel pipe off your carb and turn the fuel on. It should p*** out. Just thought i would be worth checking this as well before you go out tomorrow. It does sound like the same issue as u has with my sherco.