Small Engines (Lawn Mowers, etc.): 10 hp kohler engine, wheel horse, kohler engine

Question
I have recently aquired a wheel horse c-100 tractor, guessing about 1975, it's been sitting for about 15 yrs.
I've cleaned everything, cleaned the points, drained all old gas, carb has been cleaned and adjusted by the local mower shop (assuming he knows what he's doing). It starts with no problem. I went to use it for the first time,(plowing dirt), it ran ok for the first couple of passes, but then started sputtering with little back fires here and there. It stayed running and I finished the job, but it ran pretty crappy the whole time.Even when just driving around when not under load.
What could the problem be?
I have the serial and model numbers from the manual if that may be helpful.
Just to know ,are these engines still rebuildable?

Thanks for your help, Dave  

Answer
Hello Dave,

First off get the serial no. and model from the (Kohler) engine.  Then find a good shop manual which will list all the specifications for the engine parts (carb. ignition, spark plugs, air filter, gas cap vent, governor, etc. etc).  

Make sure there is no carbon build up in the exhaust port. Check the the choke and throttle controls to make sure they are operating correctly.

I would check that all these items are set properly.  

It sounds like possibly the carburetor or plugs might not be set correctly.  Your experience

 As long as you can find the parts, I would assume the engine should be able to be rebuilt.

Hope this info helps you out,

Howard B.