Only slow speed

[fyrekrig]

I have a MTD 420/30 which I believe is similar to ClubCadet rear engine.
Model 13B226JD308
Serial IB236B20515
DOM 02/16
I recently replaced the flat pulley (Part 756-04224) and drive belt ( Part 754-04331)
The mower was working fine for a few days then in the middle of moweing it started to slow down.
First a little bit slower and then finally very slow.
Have inspected all the belts and can not find the cause of this.
Any comment appreciated

 

[ILENGINE]

With the MTD variable speed pulley system both belts have to be replaced as a set otherwise things don't sync properly and will lead to problems. Also make sure the variable speed pulley isn't sticking in one position which will also limit your speed.