Used a friend's new (to them) 425 today. Mowed for 1/2 hour and shut it off. Had a slight run-on. Sat for 1/2 hour. Would not crank. Pulled plugs- cylinders full of fuel. Mowed for 1/2 hour. Shut off fine. Removed fuel cap and tank had pressure in it. Cap says Non Vented on it. My 425 has a vented cap. Did they change this over the model years? I also noticed a previous owner installed a shut off valve in the fuel line so I wondered if had happened before. Anyone have any ideas? Thanks.