Found my problem. I had just bought the bike, and it ran fine on the test (still cold). I had drained fuel, and done gearbox oil, but hadn't checked the radiator, as its such a pain to do on a Sherco (this is my first Trail bike). MX bike are easy, and checked very regularly.
Decided to check the ...

I have just bought a 2008 Sherco 250 with the same problem. Once its hot, it hunts.
Haven't done seals yet, but have checked everything else. Timing is 3mm BTDC, and I assume thats right. Bike also tend to Ping, so Im suspecting the 98 fuel I bought is not 98.Anyone got some answers? I cant find ...