108/3 genral help

Hi
I have a TORO 108/3 mower old as the hills but uptill recently it was great
the drive belt kept slipping so i puy a new one on ,Not an original
Now the cut is at the top height if i lower it the engine slows and belts scream

what have i done also the lever on left side does do anything????

Also when the throttle is opened over 3/4 the engine dies????
upto trying to get more power or speed from it its a great
Any help PLEASE

I live in Bulgaria so parts i have trouble getting
Any belts i take the old ones to a shop and they match them
So if anyone knows the Length etc of any belts that would be handy

Please take some photos.
European names are often different to the model names we get down here.
Hopefully some one will recognise it so we can pull the parts diagram.
Is there an identification tag on the mower ?
If so take a photo of it so we can see all of the numbers .

What you are saying does not make sense to me.
Drive belt = the one that turns the wheels
Deck belt = the one that turns the blades.

Which one did you replace ?

https://www.toro.com/en/parts/partdetails/?id=30840

operators & parts manual