Small Engines (Lawn Mowers, etc.): Drive Belt Adjustment - Poulan Pro Mower, hp model, tractor mower

Question
Poulan Pro 6 speed tractor mower - 42" 17.0 hp - Model PRK17G42ST.
We changed the drive belt, but if you depress the brake pedal very low so that you can change gears, the belt slips off. Isn't there a way to adjust this belt? It's very frustrating to get the belt back on when it slips off, over and over again.  

Answer
Hi John,

Sorry for my delay.
Make sure that you have the correct belt.  Next, check the idler pulley that sets the tension.  It may need adjustment or it's spring may have broken or fallen off.  Finally, check each pulley for excess play or misalignment.

Let me know how you make out.
Michael