Pull cord stiff on B&S engine?

I can no longer start the 6.5 hp B&S engine on my generator. The pull cord suddenly goes stiff causing me to move the whole generator sideways! The cord will fully retract. If I pull the cord slowly I can feel the compression stage of the engine so that is not seized. However, as I pull further the cord further it just tightens up hence I can't get enough speed to start the engine. HELP!