There is an adjustment for belt tension on the lower belt.
The upper ( rear ) belt has a tension fixed by the spring.
As it is a used mower , suspect everything and the most likely thing is the wrong belts bing fitted.
A plain V belt is not wrapped so when it gets warm, the rubber gets sticky which prevents the belt from slipping.
Clutching belts should all be wrapped and mower clutching belts should also have kevlar fibres.
Apart from that there is wear in the clutching system.
We really need more information as there are a lot of White lawnmowers so a modle number from under the seat would be of really great assistance.
If the tag is gone then some photos would help in identifing the model.[/QUO
TE]
Manual says Model 806
I trying to find a local supplier for the belts