Stuck needle valve?
Not that I can say with any real certainty as to what your particular problem is, but a stuck open needle and seat in the carb(s) is a usual suspect. In the future, its a good idea to turn the fuel valve off when the sled is not in use.
The other component would yes be the pump, but I'm unfamiliar with how/what would be bad in a pump to cause this. Fuel pump rebuild kits are cheap and easy, and needle and seats are easy as well.
I've had a stuck needle and seat on a lawn mower and for a quick fix I simply shook the carb to free up the needle valve, but for a sled you should really clean it out/replace the needle and seat if that is the issue.
If you're at a loss as to what could be causing this, I really do suggest buying a service manual for your sled, and reading it. Repeatedly. Makes diagnostics much easier/faster as well as provides thorough explanations of how to do anything from changing plugs to servicing cranks.
