1992 kawasaki jetski problem!?

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I have a 1992 kawasaki jetski and everytime I go to start it I have to choke it then turn choke off then start normal. after that it runs for about 10-15sec and dies. other than that big problem it seems to be fine. I am wondering what it might be? and could it maybe be because i have old gas and or oil in it?
O and for the process of choke on then off then start i have to do it every time.