cylinder probs

[tristan18au]

I own a 2000 modle YZ125 with aprox 70 hours on it. The problem is that the cylinder keeps on scuffing up no matter what i do, When i rebuild it i give it a light hone and oil the ring and bore up etc. but about 10 mins running in it scuffs up on the induction ports, They're so straight and perfect it looks like someone has used a ruler to put them there.
Could piston slap course this??
what the hell is going on, it still goes well and has compression and i am running my premix at a 32:1 ratio.

 

[tristan18au]

also could you please tell me what piston i should use out of vertex and wiesico?

 

[mackay]

Could it be time for the next larger size piston??Have you had the cylinder measured??Check your service manual it should tell you what size piston (A-D) is used for different bore measurements (the bore gets bigger as the Nicasil coating wears)
Thats just my initial impression...if you have already ensured that the piston matches the bore size then you need someone with more top end experience than me
Cheers

 

[bigred455]

Some bikes are more prone to scuffing the piston,it is not out of the ordinary,a little scuffing.If you can't catch anything with your finger nail don't worry about.