I have a Bobcat 610, they use the same Wisconsin VH4D as on some of the older balers. Parts for the Wisconsin motor are still available. Most of the parts for the 610 are still available from Cat. But ya don't want to buy to many parts that says Bobcat on it. Clutch assembly is around $415.00 for each clutch and there is 4 of them. I just replaced the fiber clutch disk in mine a month ago.
As for running rich, with black smoke, like Old said yur running way too much gas thur carb. The Wisconsin carb is not any harder to work on than those on most 4 cyl tractor motors.
If ya need it I have the Service & Repair manual for the 610. Also Parts manual.
I replaced the motor on mine, used a Wisconsin VH4D off of a portable air compressor.. I had the inner half of the vara-speed pulley machined out to fit the straight output shaft of most Wisconsin motors. I did not want to pay Bobcat $2400.00 for a new one!!! I'm like you I traded for my Bobcat, only mine was a basket case, motor blown, all 4 clutches worn out, oil lines to external oil filter shot, missing filter bracket and filter, seat missing, almost back together now, just need to rebuild the vari-drive hydraulic cylinder.
Oh by the way, to keep a Wisconsin motor from running hot, make sure you blow out all the dirt that collects in the shroud, also run some diesel mixed in your gas.
My email is open
Keith & Shawn(Gold Medal winner)