Motorcycle Repair: yz 250 blows blue smoke, piston rings, internal sources

Question
Hi,
I have a yz250 96 and have recently rebult the top end as well as replaced 1st and 2nd gear. All was good but now loses power under load. It idles fine, revs fine in neutral but has heaps of flat spots when engaged in gear. blows heaps of bluish/white smoke. Yamaha told me to replace the reed block so i got a second hand one and put it in but still no joy. Any ideas?,

thanks

Answer
Hi Matt.

Since you used a second hand reed block, you don't know how worn it really is.  A new one is what they wanted you to install.  Under the circumstances, that would be recommended.

However, there could be oil seeping past the piston rings or seeping in through other internal sources.

Start there.
Good luck and ride safe.
FALCON