I'm assuming it's pulling one direction or tracking one way or the other. Make sure your front tire pressure is balanced between 20 and 25 psi and rear 8 to 10 lbs. If the mower is still tracking or pulling one way or the other adjust the stop bolts. If the mower is pulling right adjust the left lap bar stop bolt to make it longer, if it's tracking left adjust the right until it matches up. The thing you need to remember is if you adjust the stop bolt to far the tracking can change sides so make any adjustments really fine so you don't over adjust or compensate.