When mixing it leaves black specks in the food. When I make whip cream I can see black specks in the cream.

Get a copy of the Repair Part List for your model at Kitchenaid.com
Download the following Kitchenaid Service Manual:
http://www.kitchenaidparts.be/centers/servicemanual/mixer.pdf

It covers several models including yours.
1. Check/Adjust the Flat Beater to Bowl Clearance:

Turn screw (A) SLIGHTLY counter clockwise (left) to raise the flat

beater or clockwise (right) to lower the flat beater
2. Check the Beater Shaft (Agitator Shaft) making sure the Retaining ring
is flushed with the surface of the Planetary Assembly
Constant Pulling and Removal of the beaters can cause the Agitator shaft to move
3. If the above two still don't solve your problem, follow the service manual
directions to disassemble the Planetary Assembly and check for loose screws

The Hobart H600 is a 2 horse power, 60 quart mixer, it can be used for many things in the kitchen. It can be used to make about any kind of food that needs mixed, wiped or kneaded. It works well in a pizzeria for all facets of making pizza from the dough, to shredding the cheese with an attachment, to a restaurant that makes mashed potatoes and fresh bread, to a full service bakery.
However, the biggest thing that you need to know is the capacity of the machine. As overloading the machine can cause damage that may be costly and take a technician to fix. I do not know what attachments you currently have so I will go over a few of them.

The main attachments are a Wire whip, Flat beater, and Dough hook. There are three different types a "D" wire whip (has many wires and is evenly spaced) this is used to whip egg whites, whipping whip cream, etc. The "C Wing" (has six tines in it) is used for items that are heavy for the D wire whip, like whipping potatoes or icing. The last is the "I" whip is similar to the D wire whip just with less tines. The flat beater is used to mashing or mixing examples are mashed potatoes before they are whipped, cake mixes that do not require whipping, batters and icing. The Dough hook is used for kneading dough examples are pizza dough, bread dough, etc.

The biggest thing when using your mixer is to know its capacity for the material that you are mixing. All though this is one of the bigger machines it still has limits. You should refer to this the following link for the capacity of your machine: https://my.hobartcorp.com/resourcecenter/ProductDocumentation/F-7701.pdf

There are also a few attachments that can be put on to the No. 12 attachment hub. A few of these are a vegetable slicer-grater and meat grinder.

On the tilt head models there is a "Stop screw" that adjusts how far down the head goes. I just can't remember if it's in the head or base. I use the other model that lifts the bowl.

There should be a small lever on the base in front of and below the bowl. It will move to 2 positions. It sounds like you have it set for the small bowl but are using the large bowl. Press down on the lever and move it to the other side. If I'm right, that should correct the problem.

I don't beloeve mine will turn fast enough to do whipped cream quickly.

Yes this is probably a oil leak. it can come from two possible location one of which can come from the transmission gasket that goes around the mixers center seem, if this is broken, worn or improperly seated it will need replacement. part number for the transmission gasket is 4162324. another possible location is around the cirrcular mixing gear at the front of the machine. if the seal inside the unit are damaged or worn this can cause oil to leak striaght down into the very food you are preparing. part number for the seals are 3180163. there are 4 of them, and they would require taking apart the whole unit. hope this helps.

Thanks

With the machine unplugged, remove those two black screws on the side and pull out the motor brushes. Make sure the metal blocks on the ends of the springs are in good shape. These wear out and the screws are there to easily replace them. You can order new ones cheap from kitchenaid. If it's not those brushes then the problem could be in the gearbox and you can't fix it. Are you sure it's not a bent wire whip or mixing paddle banging against an improperly seated bowl?

Do you have more than one size beaters, if you do use the smalest ones that will rase the rpm DFD

Mine did almost the exact same thing one day. I have the Artisian Model, It would do it on any of the lowest speeds. Dont know if this will help you or not but I just ran mine the next day on all the way high with the spash guard on for making whipped cream for about 6 minutes full throttle and for some reason it hasnt went slow and shut itself off since then. Mine is about 7 months old. I called Kitchen Aid but their customer service all of a sudden seems to not know english worth a poo...

Try running yours on full blast for 5 minutes with something simple in the bowl. If its a 250 watt or higher make whipped water out of 2 cups of water and a tablespoon of cornstarch. Run it till you get what looks like whipped cream. Oh yea. Use the Balloon whip. The lubrication in the motor is supposed to last for at least 5 years but I have seen on numerous post's that if you run them on all the way for at least 5 minutes the oil will even out in the motor. Running the mixers at low speed alot will cause the oil inside not to move as freely since the motor doesnt heat up the oil in the gears.

Good luck.