I have a push mower with a Briggs & Stratton engine.

Last year it wouldn't start at all. So I cleaned the carb and then it ran again. It would need a lot of priming to start, and I'd have to prime it and pull the rope 2-3 times to get it going each time I stopped to empty the bag, but it ran.

Now it starts, but after 2-3 minutes it dies. I figure the carb is o.k. cuz it runs and it has fresh gas, I'm guessing the heat is causing some kind of electrical malfunction or something. Any advice would be welcome. I don't even know where the ignition is, I'm gonna have a beer and start pulling stuff off, hopefully someone will have some advice.

Thank you.

 

The coil is located right under the fan shroud.

To make sure, right when it dies shoot a little gas or something else flammable down the carb. If it doesn't start right back then magneto is failing while hot. Not an uncommon problem.

Actually before that, try running it without the gas cap on. If it keeps running then your gascap vent hole(s) is/are plugged.

 

They're not I took the fuel tank off and it leaks like a siv

I found the coil. It looked like it was chafing up against the flywheel. I guess that would heat it up? I took it off and the part looks like its adjustable, is there a trick to get it bolted down at the right distance from the wheel?

 

a business card or about 3-4 sheets of paper is supposed to be about the right distance

 

I will try that, I need to get a carb kit first last time I cleaned it I re-used the old gaskets, so I'm gonna get a gasket kit when the store opens, then I'll re align the coil with a business card like you suggested.

 

Does that engine have a shearing pin? Does it need replacing?

 

The coil should be set to about .010" from the flywheel. IIRC, a double thickness of index card will do the trick nicely. I use a brass flat-blade feeler gauge, but not all folks have them in their toolbox.

B&S electronic ignition coils (which I assume you have since they haven't used breaker points since 1981 and there aren't a whole lot of those engines still in use) will fire just fine even if set the maximum distance from the flywheel. The spark will just be a few degrees later in the compression stroke and performance will be ever-so-slightly diminished. Closer is better as long as you understand that the flywheel will wobble and can contact the coil, eventually likely causing it to fail.
If you buy a new coil and the problem goes away, problem solved.

These coils do not fail often, but when they do, excessive heat leading to a shorted (usually secondary) wire internally is often the problem. Coil will look fine from the outside, but the internal short will effectively bypass all your voltage directly to ground instead of across the plug gap.
Sometimes the polymer casing around the windings cracks and the electricity escapes and arcs to the nearest ground (usually to one of the armature legs) instead of traveling up what is known as the "high tension lead" to the spark plug. You can't see this happening with the shroud on and it is a little bit dangerous (but it can be done) to remove the shroud while the engine is running in order to observe the coil.
Your symptoms are classic for a heat-induced coil failure. Replace it and go from there. If you have a pre-1981 engine, however, I'd suspect breaker points before the coil. They are a whole 'nuther ball game, but aren't too tricky.
Replacing that carb gasket is a good idea too, to remove fuel issues from the equation. Those carbs are about as simple as they come, especially if it is non-adjustable. I doubt you have a fuel blockage internal to the carburetor.
Let us know how it works out, please!

 

If you don't have access to the brass feeler gauges (I don't!), here are some ideas for thickness gauges:

A plain sheet of paper should be .003" to .004" thick.
A business card will be right at .009".
A 3 x 5" index card will be right at .008" to .009" thick.
A 'manilla' file folder will be right at .009" to .012" thick.

 

I cleaned up the carb and put a new gasket, changed the spark plug, filled it with fresh gas, added a little oil, and re-installed the old coil with a business card and it still won't go.

It'll start if I squirt a little starter fluid in the carb, but it dies right away.

I don't know if I did something to screw up the carb, or if the coil is bad and it's only good enough to fire the starter fluid and not the gas?

 

Please post the model, type and code number off the engine so I can see the carb type and configuration.
These numbers are stamped right into the sheet metal of the blower housing (shroud), usually just above the spark plug, but may be on a sheet metal shield over the muffler, depending on model.
Off the top of my head, I do know that one potential problem area is the O-ring that seals the intake manifold tube where it enters the carb body on all tank mounted carburetors and many gravity-fed carburetors.
Knowing the engine model will really help to give you some direction.
I don't suppose you have a spark tester? A kind of OK way to test the spark is to pull the plug, reattach it to the high tension lead, and lay the threaded shell of the plug against the cylinder and pull the starter rope to see if spark jumps the gap. The good thing about this test is that it will show if you have no spark. The bad thing about this test is that seeing spark under these conditions does not necessarily mean you have a strong enough spark to ignite the fuel under compression conditions.

I would also assess the condition of the compression components, just to rule out compression issues. Worn valves and/or seats can cause an engine to run for a few minutes then stop. You can test this by putting the spark plug back in and disconnecting the plug wire from the plug. Depending on the rewind starting mechanism your model has (the older style will not permit the engine to turn backwards unless you remove the blower housing; regardless of rewind starter configuration, you'll have to tie down the "dead-man" handle to disengage the flywheel brake unless the engine is so ancient it doesn't have a brake), you may be able to turn the engine on its side (carb up/oil fill down) and spin the blade backwards by "flipping" it with a wrist action. As the engine turns backwards, the piston will go through a backwards power stroke without the built in compression release operating. A sharp rebound (change of direction of the blade) indicates that the compression components are sealing properly and you have compression adequate to run the engine. If the blade just kind of dead-ends and stops instead of reversing its rotation sharply, you have poor compression. That is an entirely different animal to worry about than weak/no spark or lack of fuel. We can cross that bridge if/when we get to it.
Chances are that if the engine had been working fine with no noticeable loss of power or increased difficulty starting over time you have a faulty ignition coil or are experiencing some kind of lack of fuel.
Give us those model numbers and we can go form there. Be sure get all the numbers so we know its year of manufacture.
FYI- I had a customer just this year with an engine that exhibited similar symptoms on a 2 year-old engine. Long story short, the cable that disengaged the flywheel brake and kill switch had stretched and when the bail was held down, the kill switch would not deactivate, thus grounding out the coil prohibiting it from making spark. It is recommended when troubleshooting ignition problems that the kill switch be deactivated by unplugging the thin black wire from the back of the coil. Unless, of course, you have an older model with breaker points and you have to disconnect the kill wire from its junction on the side of the engine. But (and I am disappointed that I don't know this for a fact) I really can't remember if dead-man bails were installed on pre-1981 engines that had breaker points. I really can't pinpoint in my mind the appearance of these safety devices over the old shut down method of simply moving the speed control to the stop position.

Model numbers will prevent any further speculation.

 

There are small passageways in the carb that draw the fuel up to keep it running. Sounds to me that they are plugged up, which is exactly what I had to deal with on a briggs motor for my push. I had the same symptoms you describe to the point I had to take the float bowl off and clean the passageways, and now it runs beautiful

 

My spark tester doesn't fit the spark plug wire. I have the old spark plug I can bend the tip out a bit and make one? What would be the correct gap to get a good test?

The numbers are as follows.

Model - 123K02
Type - 0267-E1
Code - 03082657
Illustrated parts list from the Briggs and Stratton website.


I tilted up the mower and spun the blade. It squeaks a little but bounces back. It didn't the first time, but then I read this thread a couple more times and tried it again with a vice grips on the handle and it's o.k. now.

The O-ring between the carb and the intake manifold looked O.k. when I put the carb on. But I'm gonna have another look at the carb and see if I can spot those passages Roger mentioned.

 

The gap on the current issue B&S spark tester is set at .166". The voltage required to jump a clean gap of .166" is equivalent to the voltage required to jump a .030" spark under compression conditions (denser air/fuel mix takes more voltage to jump across than open air-think walking in a swimming pool vs walking along side a swimming pool)

Take the air cleaner out and look into the barrel of the carb and push the primer bulb a couple of times. you should see plenty of fuel squirting out of the brass jet just inside the barrel of the carb.
If you do not see fuel coming up and out of that tube, replace gasket #272653 and/or primer bulb #694395.
The paper gasket seal is critical to the primer bulb's ability to pressurize the bowl and push fuel up the pick-up tube (jet). Primer bulbs tear often these days due to the alcohol in today's fuel.
Your engine is 7 years old. A torn primer bulb would not be unexpected.

If your compression is good (seems to be according to your results) then the issue can only be spark or fuel. Need to rule out one and then fix the other.
I am away on vacation, but I'll check at least twice daily to see if I can be of further assistance.

 

You can get at the little passages without having to take the carb loose, they are the jets or such at the bottom of the fuel bowl where the screw goes in to hold the bowl on. Actually, some are in that screw. Do you have an adjuster screw, or just the one that goes in to hold the bowl on? If you have an adjuster, try turning it all the way inm, and back it out two turns, then adjust according to how it runs. Also be sure the passageway to the fuel tank is clear.

I guess I should ask, since I was thinking Tecumseh rather than Briggs, do you have the attached tank? Might have crap in the pickup screen.

 

If you have eliminated ignition issues from the equation, that leaves fuel as the culprit.
This LMS carburetor has a fixed jet fuel system-no adjustment possible.
The fixed jet is integral to the bowl nut on the carburetor. If you remove the nut that holds the bowl on the carburetor and look at it closely, you'll see that it is cross drilled and center drilled.
Small pieces of debris can lodge in that fuel passage. A very fine wire inserted and wriggled down through the center hole, followed by a shot of compressed air will typically clean that right out. A shot of compressed air through the cross-drilled hole will finish the job.The cross-drilled hole is pretty large and rarely gets clogged. The tiny center drilled hole is typically the culprit. This little orifice controls all fuel flow into the carburetor high speed and idle fuel circuits. The high speed passage is large enough that it is highly unlikely it can get clogged (except by varnish and dried fuel and corrosion if the engine is left to sit for a couple of years) The idle passage can get clogged, but usually only from sitting for a very long period too.
To thoroughly and completely clean the idle fuel passage, you need to remove the welch plug (ref. #127 on the IPL). Use a fine wire to clean the discharge holes and dribble a little solvent down into the passages and hit it with compressed air. If you remove the welch plug, you will destroy it and thus will have to install a new one as per repair manual instructions. It is not hard.
I assume that when you first removed the fuel bowl, a couple of teaspoons of fuel leaked out? If the bowl was empty when you removed it, that would indicate difficulty getting fuel from the tank to the carburetor. To verify adequate flow from the tank to the carb, pull the fuel line off the carb and turn your fuel shut off valve (if so equipped) back on. Fuel should flow freely from the line in a stream that is equal to the I.D. of the fuel line. If you have flow there, reinstall the fuel line and take the bowl off. Let fuel flow freely past the float needle valve. It should drip steadily and somewhat voluminously. If that works, you know fuel is getting into the bowl and the problem is getting fuel from the bowl up into the barrel of the carburetor, in which case you need to examine the jet as described above. It is a fairly straightforward process to find a fuel blockage using a systematic process of elimination.