I bought a 1995 Polaris Sportsman not running they put i different engine in it now it will try to run. will i need to put on different CDI box?? and how can I find out what the engine came out of

You need to call Polaris of send them an e-mail on their website. They will be able to tell you exactly which model year and model the engine came from by the serial number. They may be able to tell you about the CDI box. If everything looks good as far as the parts interchange, and timing adjustments, then rebuild the carburetor with a new float and throttle spring. be careful to put the keeper clip on the correct groove of the needle valve and be extra careful when bending the float arm for proper travel. (Motorcycle shops have a special tool for doing this if you want absolute precision.)