Small Engines (Lawn Mowers, etc.): lawn mower eng., switch problem, safety switch

Question
I have a 12 hp 36 inch murray lawn mower( briggs engine), which i got from a friend. it was smoking so i put a set of rings in it & it starts & runs fine But when i go to engage the blades the engine stalls , the blades are free to spin,the governor seems to be working fine it is pulling the carburator lever back when it is getting the load from engaging the blades.do you have any ideas on what i can do to solve the problem ,it seems like it is not getting the gas but i don't know, thanks for your help... Ray";  

Answer
Does the engine stop suddenly or seem to have too much load?

I know it is difficult to tell, but I'm wondering if there is a defective safety switch.

Try removing the deck belt from the main engine stack pulley and engaging the blades.  This will tell you if there is a safety switch problem or other problem.

Let me know what you find.
Eric