Hi,
I'm pretty new to trials bikes but i had a similar problem with my txt 280, i took the spark plug out and it had flooded in the cylinder so i turned the engine with the kick with kitchen roll over the hole where the sparkplug goes to empty it out (this is with petrol switched off). Then cleaned the plug with kitchen roll and a toothbrush, got it nice and dry and checked it for sparks.
I put the plug back in and cap back on tight, made sure connection was okay first. Turned petrol back on and made sure there was enough in the tank and tried starting it without choke if it doesnt start put choke on for a few kicks and let it off again. If it doesn't start then maybe you need a new plug...or just more new petrol?? possibly
It worked for me, hope it does for you
Jack