Why did riding mower suddenly stop starting?

Does removing the air cleaner make a difference? Sometimes mine will run but not start because of that. I have cottonwood trees in my neighborhood. Can you remove the spark plug easily to check for spark? I'd be suspicious of the fuel. The tank being empty might've allowed the tank to get dirty and the carb is plugged.

My first thing to do would be remove the air cleaner and squirt a little gas into the intake. Does it start then? If it does, but does not keep running, try it a few more times to get it sucking gas from the tank. Frequently, this will solve the problem. If not, then clean the carb.

You have an air bubble in the fuel line.

Open the tank, and blow gently into the fill pipe, cupping your hands to prevent the air from escaping the tank at the fill pipe.

Gently, so that you don't end up drinking fuel.

I had a similar situation - tecumseh engine on lawn vac - It was left outside with an empty tank. Filled it up - ran 5 seconds and died

- no restart. Dropped the float bowl - lots of water and plugged mainjet

I was hoping to avoid that, but I think that is the next step. I spent all yesterday painting trim trying to beat cold weather but today I'll mess with it.

I wish I had a fuel cutoff on the line but i don't. I meant to add one when I changed out the carburetor a few years ago. I did add a fuel filter and replaced about half the fuel line, but the tank end was hard to get to and it was 98F that day, now I'm paying for it.

That would be where I would start too. Easy to check. These things have kill switches, etc to prevent starting when it's not supposed to and a problem there could halt spark.

And that's next. Quick test is using some starting ether in the carb to see if it fires on that. Actually that might be step one, even easier than checking for spark.

The 3 riding mowers that I've owned would not crank over when the safety interlock was activated. .. which makes more sense than cranking over with no spark. John T.

My current mower has the main jet in the nut that holds the float bowl on. Cleaning it takes only a few minutes. and a piece of fine stiff wire. Wonderful design.

So what brand is your mower? What brand is the engine?

I've had the carburetor (well, the previous one) apart but it's been so long I didn't remember how to take it or the float bowl off. But I tried putting a little gas directly into the intake.

Then tried to turn it over, and a new symptom. Not even a click.

From that point on, total brain fart. Put a meter on the battery, 12.6 V. That'll usually get one or two revs even with an old battery. Nothing, not even a click. Turn key to light position, put meter on light wires, no voltage. Crap. Electrical? Acts like the seat switch isn't engaging but I can hear it click. Listen closely, and when I turn ignition switch I hear a click as the carburetor switch engages. So there's some voltage going to the right place. Futz around another half hour checking different things - make sure it's in neutral, make sure the blade handle is disengaged, all the dumb things I've done before. Give up and go inside.

Half hour later - wait, was my foot on the clutch? Go back out and try again, it started right up with the gas in the carb. Ran very rough but it ran. So it's a gas in carb problem; now I know what to do, just have to remember how.

Reminds me of the time I bought a new car with a 4 speed transmission. Drove the thing several days and no problem. Filled it up with gas and could not get it to turn over. Service station man told me to push in the clutch. I had had a 4 speed in the past and did not have to push in the clutch. I was use to putting the shifter in neutral and starting the car. That safety switch was new to me. I must have been pushing in the clutch and not knowing it.

I believe it is a B&S engine with the Toro brand, on my older Snapper mower.

IIRC, the nut is a brass 1/2" nut under the middle of the bowl which is just under 2" in diameter.

The Tecumseh carb has the jet in the bowl nut. When I removed it I saw water "balls" in the gas that spilled so I removed the bowl to make sure everything else looked OK. It did, but the bowl gasket came off in pieces - thankfully I had a spare "in stock"

Time for an update.

I tried to drop the bowl. The old carburetor bowl was held on by the nut on the bottom (that also holds the fuel solenoid). But this one had two phillips screws, and I couldn't get the back one to loosen. Access is tight and so is the screw. (and anything but phillips would be better)

But I took the nut off and could see the jet up in the bowl. I used one of those twisty tie wires to clean it out. Also I removed the old part of the fuel line, replaced it, and added a fuel shutoff valve. Getting the old line off the tank was a pain in the rear. Old fuel lines just don't want to come off, took a heat gun and a lot of prying.

Anyway, long story short, with the jet clean it started right up, I got the whole lawn mowed today.