You have a blowby issue starting. with the conventional oil your piston ring had become coked with oil residue. the cleaning action of the synthetic cleared out the coking and freed up your piston rings resulting in a loss of compressing and rise in blowby. When you acclerate the pressures inside the combustion chambers goes up and more goes by the rings and then out of the breather. my 95 stique had 92k on it when I put in a used motor with 42k on it. I have since then been using valvoline synthetic 5w30 with no prblems. I now have 131k on it never uses a drop.
