Hi Peter,

Here is the Operator's Manual for your engine:
http://bsintek.basco.com/BriggsDocumentDisplay/29lpAFKT9FzXFix2.pdf

Here is the Illustrated Parts List:
http://bsintek.basco.com/BriggsDocumentDisplay/18hruJXHnfBhU7y.pdf

The engine was built on 19 June 1995.

Black smoke is usually petrol smoke, so your engine is probably running very rich, and this may be the source of all of the complaints you listed. The simplest causes, and very likely ones in this case, are either a clogged air cleaner element, or a choke that is not opening fully when the speed control is moved away from the choke position. You can easily check both potential causes by temporarily removing the air cleaner box, and looking at the choke plate or the linkage on top of the carburetor which operates it, while moving the speed control from choke to run. You should see the plate rotate to full choke in the choke position, and to wide open in the run position. If the choke is opening fully, briefly run the engine without the air cleaner and see if the smoking has been eliminated.
Post-Edit: See later posts in this thread: this mower has the primer version of its carburetor, which does not have a choke. Testing the mower with the air cleaner filter element removed is the first diagnostic test that should be carried out.

Incorrect valve clearance is unlikely to cause black smoke, though it is not impossible. For the 120000 series engines, inlet tappet clearance should be 0.005"-0.007". Exhaust tappet clearance should be 0.007"-0.009".

Please let us know what you find.

Last edited by grumpy; 23/09/13 07:53 PM. Reason: Add post-edit