Who knows anything about lawnmowers?

It sounds as if it is an electrical problem. If there is a condenser change it with a new one. Also check the gap between the flywheel magnet and the coil. That gap is the thickness of a open match book. While looking at the flywheel magnets make sure they have no rust on them. Use sandpaper or a wire brush to remove any rust.

First off:

Thank you for all the replies!

I received far more than I expected and have a few things to try before I cut the lawn again. I greatly appreciate all the input I've received.

Secondly:

Here are the pictures of the mower. Pictures are links to the full resolution images.

As I mentioned in my opening post, I've had this mower for about three years. When I bought it, we lived in Inkster, MI, and I was concerned about it being stolen. I didn't want to splurge on anything nice, just in case. We also didn't have a shed, so while not in use it was covered up by a tarp bungee corded to it. Not the best storage, and yes, it stayed like that throughout winter.

This is the first season it's acted up like this. Coincidentally, it spent from August of last year, when we moved, through all winter in a garage. So not sure if my previous storage solution had anything to do with it.

Replies are in order of posting in the thread.

a reply to: Foderalover

Sorry, didn't see your post last night. Didn't mean to ignore you! Sounds like your lawnmower races are entertaining. Bonus points if you use tin garbage can lids as shields, broom sticks as lances, and joust!

a reply to: buster2010

That doesn't seem as bad as I would have expected. Thanks for the link to the video!

a reply to: whyamIhere

I cleaned and replaced the fuel filter when I did the other gas tank and lines.

a reply to: Skid Mark

That thought had not occurred to me. I'd say I'd check there, but it looks like I've gotten quite a few answers that could be helpful!

a reply to: eXia7

Never actually changed the oil, just topped it back off as needed. I don't think I've ever changed the oil in a lawnmower, just always added more. I'll give it a change before the next mowing.

And the compression would make sense. When I last cut the lawn it was over 85F (29C) and it ran for about fifteen minutes before starting the nonsense. Yesterday it was only 68F (20C) and it ran for almost the entire yard before it started to conk out.

Not sure if that ambient temperature difference makes that big of a difference though. It's probably more related to spraying WD-40 (and probably starter fluid at some point) into the air intake though...

a reply to: Murgatroid

First off, reading through your post and then all of a sudden Gen. Turgidson moved on me! Scared the crap out of me.

And yeah, I only get gas from the Krist (Quik Food Mart) for the small engines for that reason. Also, that station is about a five minute walk for me (Less than that if I . So that's a part of it too.

a reply to: HawkeyeNation

Glad I'm not the only one... And I'm just ridiculously stubborn. However, if I can't get it fixed by next season, that's probably what will happen.

a reply to: rickymouse

Thanks! I'll give that a shot too. Not sure if I've replaced that gasket or not, but leaning towards not.

Where about in Upper Michigan are you? I feel I've asked you that before, but hard to say. There seem to be quite a few of us from this neck of the woods on here.

a reply to: chr0naut

Happened before and after I cleaned, and then replaced all the lines and whatnot. So unless it's happening a second time with different parts, I'm not sure that's the issue. But thank you for your input!

a reply to: Murgatroid

Thank you for that suggestion as well. Seems pretty easy to do. I'll give that a shot before the next mowing.

a reply to: alonzo730

Yeah, I thought about taking it to the small engine repair. But I'm always hesitant to have other people work on stuff. Also, I'm moderately cheap. And this one is about three years old now. I bought it at the end of the season in 2012.

a reply to: verschickter

That's what I always thought about them too. As long as you keep normal maintenance it should keep on ticking for awhile.

In case you skimmed to my response to you, I've never actually changed the oil; just added more when it would get low. I'll give it an oil change before the next mowing.

a reply to: Ceeker63

They probably do have rust on them. I'll check that out too! Thanks!

Then I would change the oil first because that´s the cheapest thing to do from all the other good advices.
When you spray WD-40 into the intake and it runs better...
Normally this points towards carburator problems from what I experienced.
That was the reason on my 1972 250cc Honda and also with the needle carburetor on a cheap korean scooter I repaired.

But as you checked it and it runs for sometimes without a problem I conclude it could be oilviscosity. If you change the oil, collect something and take a photo in a clear bottle against the light.

Most part of the WD-40 will burn away as you see with the thick smoke, but some additives will help lubricating for a short time. Then it overheats again because if oil viscosity is bad it can´t reach the upper parts.

When it goes out, does it go out with a big clunk to still stand? If that happens next time, turn off fuel line (for safety).
Look at the blade and how it´s connected to the mower. If it´s only a self tightening screw, you have to look at the blades rotation. If it´s kind of interlocked with the plate below the blade, you can do this:

Swing a rope around the blade so you can pull on it. If for any reasons that thing starts suddenly (just a precaution, wont happen) you can let go. Pull slowly without impulse. Will it move? If it does, make sure you´re not just rotating the blade but the crank also. If it wont move any inch but half an hour later, it´s overheating -> oil.
For the very very low chance that the beast fires (very very low chance!) you can just let go the rope and keep your fingers.

Edit: I recommend using the airfilter again. If it sucks in a dirt, you really have a problem.

OP, that mower looks just like a B&S Quattro engine with a Pulsa-Prime carburetor.

If so your engine will not have a float bowl and you can ignore the post about the clogged main jet orifice as it will not apply.

I believe that the main jet orifice on a Pulsa-Prime is hidden behind a cylinder shaped screen in the carb that will be included with the diaphragm and gasket kit if you decide to over haul it yourself.

I believe the screen prevents the issues that the older mowers had with the main jet orifice clogging.

The first thing I would do is verify that your gas cap is venting properly.

Some mower gas caps do not have a vent but the ones that do sometimes clog and do exactly what your mower is doing.

The more likely issue though is that your carburetor needs a diaphragm and gasket kit (less than $10 @ Home Depot, Lowes, or any small engine repair shop).

It's pretty easy to do and there are several videos that show exactly how to do it (see below).

It's also possible that it's just some trash or water inside the carb but that involves taking the thing apart anyway so it's best to just go ahead and replace the diaphragm, gasket, spring, and screen since you already have it apart and the cost is so negligible.

To check the gas cap, run the mower without the gas cap and see what happens...

Check or replace your gas cap. Looks like it is not venting properly. Try it with the gas cap loose or adjust it occasionally while mowing.

answers.yahoo.com...

always check your gas cap (especially if the motor dies after running a short time). You can simply run the motor with the gas cap a little loose to see if a clogged cap is the problem.

www.city-data.com...

Keep in mind that if you see a reference to a Pulsa-jet or Vacu-jet carb anywhere those are the older versions of your carburetor which use different part #s.

Some of the links below refer to these older models.

Yours looks just like a Pulsa-Prime carburetor I believe.

Here are the videos that show how to overhaul a Pulsa Prime carb:

HOW TO REPAIR Lawnmower with BRIGGS & STRATTON Pulsa Prime Carburetor 1of2
www.youtube.com...

EDIT: In the above video the tech is seen cleaning a rubber gasket using carb cleaner, I would never do that myself personally.

HOW TO REPAIR Lawnmower with BRIGGS & STRATTON Pulsa Prime Carburetor 2of2
www.youtube.com...

Diaphragm & Gasket Configuration On Briggs Pulsa Prime Carburetor
www.youtube.com...

LAWNMOWER REPAIR: briggs and stratton pulsa prime carb overhaul
www.youtube.com...

Hi Johnnymclaneutah thanks for viewing! It sounds fuel related from what you’re saying it will start so you have spark runs good for minute or so then cuts off. Is this after you had pressed the primer bulb and it starts and then cuts off shortly? If so classic sound of a carburetor that may have trash/water and/or a worn diaphragm. Which means a good gas tank and carburetor cleaning and you will need to replace that Diaphragm as well generally after you take off that carburetor if it has any age on it best to replace the diaphragm.

Pretty sure that would be same part # 5083 not sure if your local Home store carries these our local Lowes store does. The kits has a gasket, diaphragm, spring and a new screen in the kit as well. Pretty easy to install the kit also has directions on it. The main thing is just to be careful installing the screws back in to make sure they do go through the holes in the gasket and diaphragm. These engines are solid that probably will correct your problem for around $5.00!

Hi Harry Pappas thanks for viewing! This is Part # 5083K bought this at our local Lowes Home Center right at $5.00 USD. Your engine may also reference Briggs & Stratton # 495770 Carb. Diaphragm/Gasket/Filter or # 795083 as well. This part # 5083K will fit pretty much all the 3.5 - 5.0HP engines that have this type of diaphragm carburetor mounted on top of the tank. Pretty easy to do just be careful in putting the screws back in through the diaphragm holes to make sure its not misaligned

Yard Machine Mower Carb Diaphragm Replacement
www.youtube.com...

YouTube search (Pulsa Prime Carburetor)

Some other searches that might help:

Briggs and Stratton Pulsa-Prime mower runs for awhile then shuts off - Google Search

Briggs and Stratton pulsa jet mower runs for awhile then shuts off - Google Search

mower runs for awhile then shuts off - Google Search

How To Replace The Diaphragm On Briggs And Stratton Plastic Carburators
www.youtube.com...

Briggs and Stratton pulsa jet carburetor repair
www.youtube.com...

How To Fix A Briggs Pulsa Jet Carburetor with Taryl
www.youtube.com...

Briggs and Stratton BS issues and how to fix
www.youtube.com...

This guy says that his problem was varnish in the bottom of the gas tank:

The problem with your mower is definitely fuel issues. To help you further can you tell me what kind of carb is on there? Is it the float type carb or a vacu jet carb that's mounted right on the tank?

What you have then is a vacu jet carb. Take the tank and carb off of the mower by taking off the two bolts and the throttle linkage. Then drain the tank and take the carb off of the tank inspect the diaphragm and gasket for cracks or holes and to make sure it's not stiff an that the spring inside the carb is in good shape. If not a diaphragm and gasket kit is easy to obtain for less than 10 bucks. Clean out all holes in the carb and tank. Reassemble if it still won't start the carb is at fault and a new one runs around 20 bucks. Remember if you run the mower without the air filter you must still thread the bolt in that holds the air filter and cover on for the engine to run properly.

Looks like it was the diaphragm. Lowes.com says my local store has the gasket/diaphragm kit in stock for $2.98 so I'll be picking that up today.

The bottom of the gas tank was Very varnished so I soaked that for a while. Cleaned more, blew out with more air, reassembled, and it fired right up on the first pull!

Re: B&S 500 series motor won't stay running
www.lawnmowerforum.com...

A few more links you might need:

Carburetion Troubleshooting Quick Reference Guide [PDF]
www4.briggsandstratton.com...

Lawn Mower: START & STALL Solution! (Step By Step)
www.youtube.com...

How to fix Briggs and Stratton lawn mower engine that starts and dies.
www.youtube.com...