Different physic behaviour when use @MenuItem

Hi, I have a code that generates a simple rope like behaviour. When I attach that script to a gameobject and push play button, the rope is created and starts to oscilate. Now I want to create a MenuItem in order to create the same rope in the editor. I have copied and pasted exactly the same code (deleting the Start() function where it was). As a result the rope is created but the movement is totally different, it is stretched much more. The value of the different components (rigidbody, hingejoint, etc) are the same in both cases. Does anyone know why this happens? Thanks a lot