I have a 2001 yz 250 that i bought off a guy. His word was that it has brand new top and bottom end in it, but i keep fouling plugs and my buddy said i might need to do crankseals. Does that mean crankshaft seals and bearings or what? I dont know much ive only owned trail bikes until now so i havent had to tear down an engine. Im mixing 40:1 and it fouls plugs when im riding the bike just bogs out and the plug is really wet and black. I know its got a new jug on it and head gaskets but the rest is a mystery