About 2 months ago I bought a 2003 KTM250EXC racing with 120 hours on the clock. Done about 10 hours on it since then with no problems. Until yesterday!!! Left home 8am, bike started on the button and called in to top up with fuel. About 4 litres, Shell Optimax as usual.Got on bike, took about 10seconds of turning over before it would fire-very unusual. Rode bike for about 2 hours with plenty of stopping and restarting without a problem. Then after a slightly wet lane the bike cut out after about 15 seconds of being on tickover. Took about a minute of turning over to restart and then wouldn't tickover or pull away unless very gentle on the throttle. As soon as I tried to accelerate hard it just cut out again. This happened another 3 times before I finally got the recovery people out to get home. Symptoms are Start great from cold first turn, after a few minutes on tickover it cuts out. Then a b*st*rd to restart. When it does restart, if you try and rev hard straight off tickover it cuts out. But if you build up slightly slower, it will rev as normal. So far today I have-stripped and cleaned carb-nothing wrong. Checked feul cap vent-OK. Checked feul-no water contamination or dirt. Plug-dry black sooty colour. Air filter dirty but not blocked,-cleaned ,oiled and refitted. Still got the same problem. Any ideas??????HELP!! Cheers Tony.