Is there a way to tighten the self propelled belt?

[2.7]

My mower doesn't move forward anymore. The belt is still present and not broke it moves as well, but it's not tight enough to propel it.

Any DIY? I can't find anything online about tightening the belt, only replacement.

The mower is a craftsman 650 series 190cc

 

[Grassbandit]

Replacing is best, but also check that the cable that engages the self propel system is moving freely.

 

[msaeger]

Is there a tensioner on the belt?

 

[Grassbandit]

Is there a tensioner on the belt?

there isnt a tensioner on the belt, what happens is when you engage the system a horizontal wheel moves to engage the belt (parasitic load) and then the wheels will turn.
Another issue I notice sometimes is that the gears/teeth on the inner side of the deck wheels gets worn and therefore they won't spin.
So check: 1 cable moving freely 2 belt wear 3 deck wheels

 

[SONOFADOCKER]

Take the two drive wheels off . You might see that the plastic teeth have worn away .
I need to change my drive wheels every few years ( bumpy lawn )
You can get wheels on eBay less than sears parts center .
Wheels come off in a few seconds with 9/16 socket.