1. Equipment: Push Mower 2. Brand: MDT Yard Machine (2000 Model) 3. Engine Make: Briggs and Stratton 4. Engine Model: 12H802-3509-B1 (6.0 HP Quantum Engine) 5. Issue Description: I’ll start by saying that I’m new to working on small engines, so I’m learning as I go. Currently, the mower won’t start if I have the air filter in the mower. It starts to fire up, and putters for 3 to 5 seconds and dies. If I remove the air filter, it fires up and runs fine. After letting it run for about a minute, I shut it off, put the air filter back on, and it will fire right up again. Once it’s sat awhile, I have the same problem again. I should note that I replaced the carburetor, spark plug, fuel line, and air filter. I have a new gas tank on the way because the current one leaks fuel from the top seam. It really seems like it’s an issue with air flow since it will start and run fine with the air filter removed, but I’m also not sure why it would start with the air filter back on it after it’s been running a minute either. Like I said though, I’m learning as I go. Any suggestions would be appreciated.

As a retired mechanic I have seen many changes in fuel over the years but the "latest" change has to be the worst. Ethanol is a viable fuel as long as the engine it is used in is designed for it but when it is introduced into gasoline it will encounter materials that are not designed for it's presence. In two stroke engines in particular the plastics are not always compatible with it's properties and the results can be devastating. My Poulan chainsaw got to the point where I had to use waterpump pliers to remove and replace the gas tank cover as it had swollen that much. Fuel lines will rot with just a few months when exposed to ethanol. I did find a "fix" in the guise of ethanol free gasoline. To be exact I am feeding it 110 octane racing fuel. After less than a month of use I can now remove and replace the cap by hand and the saw runs super. No, high octane fuel does not run hotter but actually cooler. It is not cheap though, $8.49 a gallon but a gallon will last a long time for a homeowner saw and the advantages out weigh the price.