Small Engines (Lawn Mowers, etc.): Engine dies when blades engaged, engine model type, speed needle

Question
I have a 1977 Montgomery Ward tractor with a 16hp B&S motor.Very well maintained cranks easily. Problem is when the blade is engauged the engine revs then stalls or dies. It has 3 pulleys on front of engine, two on the bottom front of frame and the large belt wraps around these to the three blades on the mowing deck. Is there too much tension on the belts or is there some adjustment on the carb to keep it from stalling? I can pull on the belts and they have play in them. I engage the PTO(blades) slowly, when it starts to die I release the blade and the engine rpms go up and down rapidly until the engine dies. Sometimes I can push the idle lever down to "slow" and it will stay running. After this it is very hard to start the engine again.

Answer
Most likely the problem is in the carburetor.  There should be an adjustment on the carburetor that might fix the problem.  Try turning the high speed needle out 1/8 of a turn.  I would tell you exactly which needle it is, but I will need the engine model, type and code number.

Have the points been changed recently?  The spark plug?  Fuel and fuel filter?  Finally, did the problem happen suddenly or has the mower sat over the winter season?

Let me know.
Eric