Every time I put gas in my tank the car takes a while before I can get it starte

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Every time I put gas in my tank and then I put the key in the ignition and turn the key the engine sounds like it's trying to kick in but it doesn't hold. I have to keep turning the key on and off before it kicks in. Once I get it started it's fine. I never have a problem starting it up until the next time I get gas. What are somethings that could be causing this.