Check the front wheels. I have the same problem and one of the wheels is locked which keeps the mower pulled in that direction. I am trying to figure out how to get the wheel loose.

If the front wheels don't freely rotate in a complete circle, they may be binding up on the front metal piece between the wheels. if you "bump" into a tree or something, you can bend the edge downward and have it impede the free movement of the wheels...there may be other problems as well but this is just about the locked wheels...hope this helps!

With both handlebars in full foward position, the machine pulls to the right. How do I adjust this