The Minarelli identification info is on the bottom of the engine and can be seen when looking from the right hand side.
My original Italian Owner's manual says to use a 3% mix. That equates to 3.8oz to a gallon of gas (or 33:1). With synthetic oil you can probably run thinner than that, say 3oz to a gallon which works out to 42.6:1
Is the engine stuck? Or can you still spin it over?
Do you have spark?
Have you cleaned the carb?