Hi guys, I just have mine 08 rebuilt with the 04-05 KX250F piston (by Wiseco) installed, which has 13.1:1 ratio. Valve timing, clearances, spark... look good.
However it seems much harder to start. I could make it firing up only few times since, whenever it starts, the engine sounds normal and smooth.

Do you have any experience on using that old model piston? And could that lower ratio 13.1:1 be the problem on starting issue?

Thanks in advance.

 

Updated: my KX new top end seems good to go. The new combination needs more time to really breakin and now after 2 hours, it starts easier and everything works properly.