Ok so I bought this 98 kx250 that needed a crank seal. So I tore the motor down to do a replace the seals and ended up needing crank bearings and a piston. But anyway I got it finished and started it and it ran perfect but then the throttle cable broke. So I bought a new one and now the bike doesn't run very good.its very boggy now.and the weird thing is it will only stop if you pull the mixture screw completely out. Any ideas of what it might be.it also is blowing black oil out of the exhaust.