Small Engines (Lawn Mowers, etc.): MTD variable speed drive problem, variable speed drive, variable speed pulley

Question
I have an MTD Yard Machine lawn tractor model 13AQ670H088 (TMO-314600), SN 1K196H20176 that won't get up to speed.  In the beginning it would slow down after I had been mowing for a while.  It would finally come to a stop unless I shifted to high gear.   Pushing the clutch in and out would get me restarted for a few moments.  Now it is slow in all but very high gears, and it also smokes the front belt if I keep going at lower speeds.  I have replaced the engine pulley and the rear belt idler tension spring.  I also replaced both drive belts with OEM belts.  I removed, inspected and lubed the variable speed pulley and made sure the floating sheave is moving free.  I have also verified that the rear belt idler is spinning free, not running hot, and not catching on something.  I even doubled up the idler tension spring thinking that would surely help, but it didn’t.  I think I have the speed control adjusted correctly, although the owner’s manual that is available on the MTD website for a model 600 is actually for models 660 thru 679 and describes a speed control that is a bit different than mine.  I don’t see any missing parts.  I also dropped the mower deck to reduce the workload, but that didn’t change anything.  This one has me baffled.  Any ideas?  Could the transaxle be causing a problem?  The variable speed pulley sheaves look ok, but could they have wear that isn’t obvious to me.   Or what else?

Answer
Hello Jim:

You can View a Breakdown/IPL of this Unit at this Site Addy, http://www.smallenginepartswarehouse.com/parts.asp and Select the Shop Online Parts Look Up. Then Select the Model Tab. Then Select the OEM (MTD)  and Enter the Model Numbers 13AQ670H088. Then Double Click on the Model in the Results Area. Now you can Select the Section of the Unit you Wish to View. Select the Drive/Frame/Pedal Assembly/Wheels. Check the Variable Speed Pulley Bracket. Make Sure it is Moving Freely and is Not Binding when Moving. Check the Variable Speed Pulley and Make Sure the Center Sheave is Moving Freely between the Outer Sheaves. From your Description it Sounds like the Belts Require Replacing and the Variable Speed Bracket or the Variable Speed Pulley is Binding and Not Allowing the Spring to Keep the Proper Tension on the Drive Belts. This Does Not Describe a Transaxle Problem. If you Hit a Snag or this Does Not Correct the Problem,  I am Here if You Require More Assistance. Hope this Helps. Let me Know What Happens, Please. Have a Happy Holiday Season and May the All Mighty Bless You and Yours. Be Safe and Happy. Thanks.

Good Luck

Respectfully

John

PS: I am Allowed to Answer 10 Questions a Day. If you See I am Maxxed Out, then Try Submitting your Question at or Just After 8pm EST (US). My New Day Starts then. Comments and Ratings are Greatly Appreciated. Thanks.

Respectfully

John