won't start

hey dudes.... this is my first post.... i have a 125cc TDR DUCAR GENERATION II ENGINE, 4 Stroke HIGH PERFORMANCE SingleCylinder, Air Cooled, Unleaded Petrol Only.... bla bla thumpster and Willy took it ridin' and now it has trouble starting. i put new fuel in it and a new plug... it...

i'm hoping someone has some advice on this one for me. i pulled down the head and cylinder last weekend on my lifan 140. it was starting like a pig (taking 5-10mins of kicking the thing) but running fine once going so i figured there might be some issues with the valves not sitting completely...