Small Engines (Lawn Mowers, etc.): Lawn mower drive unit not working, cycle model, operater

Question
Have a very old Lawnboy 2-cycle, model 8155.  Put a new belt on it this spring.  Adjsted idler pulley to make sure it engages drive unit when handle is moved forward.  Also adjusted cable to drive unit to ensure it is fully engaged.  While all seems to be adjusted fine, the unit is very sluggish when moving forward.   (carb is set to fast speed also)  Blade rotates fine, but the operater needs to "nudge" the lawn mower forward to get it moving.   Also on a small hill, it needs to be "helped".  Any thing else I should adjust/fix?   Thanks much.

Answer
Is the belt a Lawnboy belt?  You can adjust the ilder pulley to tension the belt but most likely if the belt is grabbing the problem is something else.

Is the ilder pulley bearing wore?
Has the rearend/transmission every been serviced?

Let me know.  
Eric