Small Engines (Lawn Mowers, etc.): Lawn Riding Tractor Speed Control, speed control lever, variable speed pulley

Question
I have an older MTD Transmatic Front Engine Lawn Tractor Model # 139-613-372 and am experiencing a problem with the Speed Control. The tractor is stuck in a very low speed regardless of where I place the Speed Control Lever.  It seems the problem may have to do with the Variable Speed Pulley mechanism.  It may be frozen in the slower speed position.  Can you shed some light on what steps can be taken to determine the exact problem & how to rectify it?

Answer
Most of the time the belts need to be replaced...both belts.  They are easy to replace compared to Murray variable drive mowers.  I believe the rear belt can easyly be put on from the top, just remove the panel between the are where you legs go.

Mark the pulley top if you have to remove it...this way you can't put it on upside down...just to be safe.

Let me know if the belts fix it.  I have never replace the pulley, but they can go bad.  Check the pulley needle bearings and the shaft it rides on for wear.
Eric