First, I was mowing and suddenly my Murray MT155-42" cut mower starting losing rpm's ,still cutting mind you, it didn't backfire, jolt or sputter just slowly lost rpm's ,i then disengaged belts, it gained a small rpm's back then went down again till it went dead about 75 feet further as I headed back to shed.It hasn't cranked since. I initially thought fuel.I checked fuel lines, ok. Checked bottom of carb with the wire harness plug on bottom, fuel ran out good. So, I thought electrical.It fires at the plug.I tried starting fluid spray, no backfires, no combustion.So I then remembered the shear pin or key at the magneto head disk thingy,lol, not sure what to call it. It seemed fine. No backfires remember. So, now Im back to my first thought of fuel.So ,I already checked fuel at carb so could it be water in fuel.And why wouldn't it even try to crank with starting fluid? Is a switch keeping it from sparking? Thanks for reading my large post.Just wanted to be thorough.
How old is the fuel? Ethanol fuel can go stale in as short a time as 6-8 weeks. What happens is that the ethanol comes out of solution with the gasoline and all of a sudden the engine gets a couple of tablespoons of pure alcohol... which a low compression engine simply can't digest. I HIGHLY recommend draining all the old in September and starting with brand new, just purchased fuel in the spring. Pour anything over 6 weeks old into your car, which has electronic fuel injection which can burn junk fuels. So what's in your tank may look good to YOU, but it can't fool your engine.
Water. Did you hose off the mower this Spring ? It only takes 4 or 5 drops of water to collect in the bottom of the float bowl to stop the flow of gasoline to the engine.
Starter interlock switches may have told the engine you had left the driver's seat or applied the parking brake... when you didn't.
Remove the fuel cap and see if it starts. The EPA fuel tank breather on newer mowers can easily clog (due to the effects of ethanol fuel). When air can't enter the tank, then fuel can't flow out of the tank due to simple vacuum. So the mower runs out of fuel, but can easily crank the next day after air leaks in.
