please help 2004 yz250

[dbrace]

I have an o4 yz250, that is dead stock except for a pc silencer. It runs awesome untill it gets hot.

After about 5min of racing it begins to surge and detonate real bad and becomes real lean. I know it's not jetting related as i rode at the same track the day before, same temp and fuel etc and it was perfect all day. We put in afresh plug, cleaned the carb and visually checked all the electrics.

With fingers crossed i lined up for the second moto and pulled a top three start in a field of 450's and again the bike ran great for about 5 mins and then the same thing happened nearly sending me over the bars, i decided to call it a day.

Any help would be really appreciated.

Thanks.

 

[showtime586]

I can't recall ever running across that situation before. I am wondering if it might be temperature related, given the fact that it will run for a while.

 

[_j0kA_]

check to make sure there is coolant in the rads! open the rad cap and start the bike, look to see if the coolant is moving - if not something is either blocking your water pump or its broken

 

[ben.handasyde]

where in aus do you live