Craftsman garden tractor/ 26hp kohler V Twin?

It starts and runs smooth at first w/choke on. Then starts flooding out but stays running as long as you keep moving the throttle and choke back and forth. Then it will run smooth again for about 15 or 20 seconds, then it floods out again. It'll keep running like that for as long as you want. Smooth/flood/smooth/flood. AND while it's flooding, a foamy oily substance oozes out of the fuel pump through what appears to be some kind of ventilation hole with a small screen over it. It's about mowing season. Can someone please help? Thanks