Plugs look great! Something rubber in the PTO? Crank seal?

Post a pic.Lots of soot will typically lead you to a belt fighting w/ something it shouldn't be or a excessively rich exhaust.

Some pics.......

more pics

Hopefully y'all get the idea now.

If the engine was running rich (choke or carb problem) I would think one would smell it or the plugs would be gunked up. The plugs are PERFECT!

You better get under the tractor and check all the belts routing because the "soot" looks like it ain't soot at all.
Genuine soot from the exhaust will have a greasy composition and is somewhat stubborn to remove (usually requiring solvent or detergent).
The stuff on your Sim looks like it brushes away readily when touched, and that usually points to belt material.
Now, it is possible that something has gotten "into" the plastic cooling fan and/or the fan air intake grille on top of the engine and what is being trashed may be the plastic fan and/or intake grille.
You surely want to check out that possibility before it's too late.
If you don't see anything obvious just by looking at the plastic intake grille, remove the flywheel/fan cover and inspect everything under the cover.

Thanks mownie, I was hoping to hear from you. I called it "soot" because I didn't know what else to call it. I'm mechanically inclined enough to think that's it's not an engine issue because the exhaust doesn't smell like anything...especially exhaust where the engine is running rich.

Going back out now to re-check and triple check the belts.

Is the shield around the muffler such that it can entrap grass, which the smolders when the muffle gets hot?

I had a panic situation a couple of years ago when that grass went from smolder to a fire. Fortunately I was able to get it out with no damage to the tractor.

Is there a accumulation of grass near one of the pulleys or near a belt that is becoming hot from the friction?

I just got done doing the following:

1. Removed the fan intake cover and everything looks good.
2. Completely cleaned off the top of the deck with compressed air.
3. Cleaned off several surfaces of the deck so no more "dust".
4. With deck attached, drove around yard several times. No dust buildup.
5. Mowed several passes in yard. Yard is VERY bumpy. Dust started to show on the deck.
6. Stopped moving. Let deck run at full speed while tractor stationary. NO dust buildup.

OK....so I'm thinking that the deck belt is rubbing on something while the deck is bouncing across the yard.

BUT...I had checked all the belts and they looked OK to me.

I pull off the deck hoping to find a chipped/damaged pulley that could be causing the belt to wear. NOTHING!

Lifted the front of the tractor to get a GOOD look underneath (again). NOTHING seems out of the ordinary!

I am at a total loss of what it could be! I've publically stated that I wish the tractor would blow up so I could go out and get a tractor with a 54" deck. Maybe the internet God's are giving me my wish?

Your simplicity deck is the type that "stripes", correct? If so, that means that the deck rear rides on rollers touching the ground... rather than just being suspended from the tractor's frame.
Add that to your bumpy yard and you may have a deck that is having to move up and down a substantial distance during normal mowing - possibly more than it is designed to do..?
Another question - Are you running an OEM deck belt setup or aftermarket stuff?

rcbe - OEM deck (yes to stripes) belt and I've been mowing this yard for 2 years. This dust problem started about a week ago.

Maybe a guide out of place or possibly the traction belt system uses a composite idler that is in less than noticeable spot?

You may have black mold or they call it slime mold on your lawn. Easiest way to find out is stretch your garden hose out, stake one end of it and with the other end walk around in a circle while dragging the hose on the ground. After one or two times going around with the hose, check it and see if you have the "soot".

Just a suggestion.

Forgot to tell you to do this while the grass is dry.

I am a retired greenskeeper of 30 years. I have only seen this once in that time period and it was on my own lawn. The mold will go away and will not damage your lawn. No treatment is necessary.

This post was edited by always-beezee on Sat, Aug 17, 13 at 10:44

I think the problem may be in fact black mold! Yesterday after putting everything together and mowing, the black dust would literally come and go depending on where I was mowing my 1.5 acres. When I was done mowing I could blow the entire tractor clean using only compressed air.

I'm going to try always-beezee's test ASAP. Will keep everybody posted.

That certainly is a logical explanation.
I would have probably never guessed that the stuff was mold spores.
My general experience (limited) with mold and other fungi is that they require (usually) a generous amount of water/moisture/humidity in their early stages of development.
So I researched the subject and find that always-beezee's suggestion that the source may be slime mold is probably on the bull's eye.
Apparently the black stuff is spores (analogous to seeds) that are designed to be spread by the wind.
I can't think of a better dispersal system than that provided by a lawn mowing machine.

If the garden hose trick doesn't get any results, try another mower. A push mower or ask one of your neighbors if you could borrow their's for a little bit. The mold could just be in a small area of your lawn (1000 sq. ft.) or the entire 1.5 acres.

I am pretty confident that the slime mold is your problem and not a mechanical problem.

I know that this is a few months old but I am curious as to what the problem was.

So if 1111GD1111 is still there, tell us please.