Small Engines (Lawn Mowers, etc.): Montgomery Ward Garden Tractor Engine Problems, vertical shaft, horizontal engines

Question
I am having trouble with by Montgomery Ward Tractor.  I start it up and after about 2 minutes the engine acts like there is no gas in it and the engine speed goes up and then back down and eventually the engine stalls.  No matter what speed the throttle is set at.  Every time I check the spark plug it is dark black and then I clean it and after about a day of use the spark plug is black again.  Do I have a carburator problem?  Do I have the engine speed set too low?  Where is the Intake Manifold located?

Thank You  

Answer
How old is the mower?  If you have a single cylinder engine there is not manifold.  If you have a twin cylinder the manifold is under the carb.

It sounds like the carb is running rich.  Is the eninge a horizontal or vertical shaft engine?  I'm guessing the tractor is an older model.  Some of the old horizontal engines used an up-draft style carb.

Have you recently tried adjusting the carb?

Let me know.
Eric