Riding mower tighten deck belt?

I have a white outdoors 20hp 42" deck riding mower. It has a manual pto lever.
Firstly, the lever seems very stiff to turn on.
Secondly, the belt just looks loose when engaged. It mows fine in the dry but sometimes I drive though a wet patch on the land and the belt slips and then smokes so I have to disengage it. I can't see anyway to tighten or move the front pulley. Is there anyway to tighten these?

 

Sounds like your tensioner arm and blade brake pivot points are rusty and not moving freely or travelling their full length. I recommend spraying them with pblaster and work them back and forth, especially the blade brake arms.

 

I may be off base, so take this only for what it's worth. I think that yours is an MTD product, and and I have a similar size MTD/Bolens at my cabin that I had a similar problem with. As far as the deck, as Cheese said, make sure everything is moving freely. The belt, on the one that I have anyway, has a lot of play, even when everything is tight, so there isn't much leeway for anything to not be working at its' full level. As far as the PTO, the cable on mine goes up and over a pulley, under the dash where it is very difficult to see or even feel, and the problem I had was that the side of the pulley wore down, allowing the cable to walk off of it and bind up. I replaced the pulley once, another OEM plastic or nylon or whatever, and only it lasted a season or so before the sides of it wore down enough to allow the cable to flop off again. The second time around I scrounged up a metal pulley, may have been brass, made a hooped guard for it to keep the cable from flopping off if it got slack, and that has now worked for 3 or 4 seasons.

 

I agree with cheese although if it is not corrosion there is a bushing under the pulley that the tensioner arm arm pivots on, that may have worn.

 

I don't see any tensioner arm.
When you engage the PTO, it releases the breaks and kind of moves the whole mechanism, which tightens the belt to the front drive pulley and therefore all the other pulleys. Is that the arm? I can't see any way to tighten that.

 

The belt doesn't want to tighten around the pulley on its' own, so something is being pulled by a spring to cause it to tighten. Do you have the owner's manual? Or is there a decal with a diagram of the belt on the deck? You might be able to look at one of those and see a tensioner. Then it's a matter of seeing if that is moving freely, or if something is bent or whatever. I have gotten manuals for a few MTD products from their website.

 

The tensioner arm is the arm with the tensioner pulley on it. It is the arm that moves to put tension on the belt.