I recently bought a 1995 MTD lawn tractor. It has a 12.5 hp briggs&stratton industrial/commercial engine.The model # is 289707 and the type # is 0154 01. I brought it home and used it and it ran perfectly for about 30 minutes. Then the motor started to bog down under load until it stalled. I restarted the motor and it was running terrible and as soon as I would turn the blades on it would bog down again and stall. I replaced the air filter and fuel filter. I also replaced the spark plug and made sure the gap was correct. I cleaned the carb and removed the bowl to make sure the float wasn't sticking. I cleaned the bowl and put it back on and still no results. I thought maybe the fuel line was collapsing so I put new fuel lines on and it's still not helping. I even put a longer exhaust pipe on because the muffler is about 2 inches from the carb and I thought maybe it was heating the fuel up and still no results. When I run it after it sits, it runs fine for anywhere between 5 and 15 minutes before it starts to to act up. I'm stuck. I would appreciate any advice that any of you might have. Thanks in advance, Mike.

Check fuel cap for proper venting, or to test to see if this may be your problem, run it with the fuel cap loose and see if the problem surfaces. From your description it sounds like a fuel issue, but since it runs good for awhile it could be something is interrupting the fuel supply.

I just tried running it with the gas cap loose and got the same problem. Ran good for 5 minutes and then it stalled. I even removed the gas cap and it still didn't help. The fuel tank is clean and the filter is new and I removed the filter and there wasn't any signs of obstruction or contaminents. I'm out of ideas.

Well it does kinda sound like a fuel issue, but it could be ignition as well. Test for ignition spark immediately after the engine dies and see if you have any. It may be your ignition module failing.

I checked for spark and it looked good. Do you think it could be vapor lock? The exhaust is right next to the carb. It has the plain old black fuel line on it (brand new.) And if it is vapor lock, why would it start now? Wouldn't it have done that even when the motor was new if its caused by heat from the exhaust? I'm really starting to get frustrated. :confused:

There is a possibility that the problem could lie in the valves. You may want to check the clearances, and look at the valve seats, perhaps one has come loose in the engine block.

I just bought 13.5 HP B/S that the gas hose had swelled shut on the end side.Changed that And thought I had a good mower but think the guy turned or messed with every thing he could fine to turn.Still trying to get it to run.