I have might have overlooked this but if you using after market belts that may be the problem as they would be of the wrong dimensions.
The current OEM belt specs is LGTH = 2635 mm, TK = 10.9 mm, WIDTH = 14.4mm. That would make the belts about 9/16 wide. Most after markets would be 13mm wide( 1/2" belts). So I would think a slightly shorter aftermarket Kevlar would be needed. Something like MTD 954-04219 (1/2 x 103.25)(Rotary 12790, Stens 265-216). This would basically be only a 1/2 shorter but would offset the width problem as the belt would sit deeper in the pulleys.
And burned sections of the current indicates jamming or slippage. A 102 is just plain too short. Deck clogging with is one possible source