I recently upgraded my trusty 2004 yz250f to a 2007. I moved my 290 kit to the new bike and put a fresh piston and rings in the old 250. For the 290 on the new bike I just put in new rings and gaskets. New bike with 290 runs good, but now smokes a bit. I did not notice until about the second time I warmed it up, but when you crack the throttle it puffs out blue smoke like a two stroke. No visible smoke other times. I probably have run it about 1/2 hour and everything feels OK, except for the smoke. Now the oil rings are pretty thin, and it is possible I garfed one on the assembly. Before I tear back into it and burn a $60 something gasket set, has anyone had similar smoking after a rebuild and had it clear up? Before you ask, yes - the ring gaps were staggered.