07 kx250f knocking

[bigbike]

The other day, my sons bike overheated. There was blue smoke and a burnt odor. From looking at the plug, it was running very lean. I relaced the rings and the main jet but there was a knock in the motor and still running lean.
I check further and found some play in the connecting rod big end and the left crancksaft bearing. I put in a hotrod crank assembly and oem cranckshaft bearings. I still found a bit of play in the left bearing even if it fit thight on the crank and in the crankcase. After re-assembling, I still have the same knocking and still runs lean. I double checked timing chain and everything. I starts and runs good. I tried another crankshaft bearing and it still has some play. Is this normal? If so, what would be the knocking noise?
THANKS!

[deuceshigh7]

well the rod should have left to right play, but up and down play is bad.. don't know which motion u are referring to but what happened to mine was that the bearing housing cracked and was allowing the rod and bearing to slide around...

if u are running lean, take apart the carb and do an overhaul on it with some carb cleaner and compressed air, there might be something stuck in one of ur jets...
-nic