I have a 1987 Grasshopper 1212 with a 44" deck and 12HP Kohler engine. It will shut off after 15-20 minutes of mowing and I let it sit for about a half hour and it just continues to repeat the cycle. I got it from a family member who had let it sit for the last 2 years but used it every week for the 2 years previous. He rebuilt the engine when he bought it. I took it to a local grasshopper dealer and they replaced belts, chains, blades, air filter, oil & filter, and greased it all up. Before I sink anymore money into it, I want to first see if anyone has any advice. I think it could be overheating, causing the cylinder to expand. I know that if that is the case then the motor will eventually cease. I know how hot mower engines can get but this one seems to get extremely hot. I replaced the spark plug because the old one looked a little foul. I had all this work done to it before I started using it so the dealer did not know about this problem.