Why won't my Craftsman 6-0 Briggs & Stratton lawn mower stay running?

Question

My Craftsman 6-0 Briggs & Stratton push lawn mower will not stay running. If I keep pushing the primer it will stay running, then when I stop pushing the primer it dies. I cleaned the carburettor and I still have the same problem.

What is causing this and how do I prevent it?

Answer 1

We've been trying to hammer the solution to this issue to our customers since B&S & many other manufacturers, switched to their aerodynamically shaped fuel tanks for esthetic-reasons, mainly to match the new OHV engine styles. In doing so they knowingly created a nightmare for owners of same equipment. These tanks have a domed-like top, & various baffles & wells molded into the bottoms of the tanks. These features, combined with, ANY moisture AT ALL, in the air, WILL create the issue the OP is dealing with.

Owners believe & insist they never use old fuel, or, "it's new fuel," "they just checked/cleaned the carb," etc., etc., etc.. It doesn't matter how well you care for your fuel. The one solution is to ALWAYS keep the tank as full as possible, but this does not assure a total fix.

Engineers assumed their fancy tanks would be the wave of the future. Together the domes & the wells create the perfect "condensate creator + water storage system" which, once the wells are full of water, begins the nightmare. 1) Condensation collects inside the tank in the domes. 2) Vibrations and equipment movement shake it into the fuel. 3) Inherent liquid densities cause the water to sink into the wells. (One of which is also the location of the fuel line to the carb.) 4) In average to high humidity regions, it's typically about one year before the problem shows itself. Dryer climates may never see it occur. 5) Consumers often go in & drain the float bowl, (correctly so) but neglect to clean out the tank. Worse, since the tanks have several of these wells in them, you can't just pull the line and drain it, for the other wells will hold their built up water. (We've occasionally drained them, and blotted up the visible water with a clean rag attached to some sort of poker.) 6) Temporal fixes (draining the bowl & using the equipment until the bowl refills with water again) are responsible for a secondary stage of the problem. e.g. Eventually, the jet/pickup tube that the carb float bowl plug screws into, will become corroded & or, partially plugged. Oft times the actual jet is in this plug, thus, leaning out the fuel to the engine & creating the, "runs when you prime it" example of the OP.

You can use a tiny wire to gently scrape away this corrosion in the plug/jet, as well. Those carbs where the jet is in the pickup tube screwed into the carb body, you'll have to remove the carb & use a similar wire to clean out the tube & its tiny orifices inside the carb body. If the bowl was punched out of Chinese steel, it'll rapidly exhibit un-repairable corroded-thru leak point in the bowl. (new one, or try JB weld.)

Nonetheless, trust me when I tell you, (post-multiple thousands of dollars to do this semi-simple work for customers) these systems need routine cleaning. Also, contrary to popularly offered wisdom, you never want to leave these "drained" in the off season. You should fill them to the brim, and if possible, start them once or twice in the off season, & cap off the tank again.

I (could) offer names of B&S employees who've told me, this was a KNOWN design flaw, and yet, they've left it be for decades in some cases. One of our habitually condensation producing machines, I finally grew tired of and ripped the plastic tank off and installed an old steel tank on it. After several years, never had another condensation problem again.

Answer 2

It needs be noted:

1. The OP is asking about a 6hp Briggs. (i.e. it is a four stroke engine)
2. The OP's engine (unless someone went through painstaking retrofitting of a different carburetor) does not have a two-stage adjustable fuel mixture system. More than likely, there's NO adjustments at all for fuel-air, and only one external adjustment for the idle speed?
3. On the matter of sharpening blades:
   You ABSOLUTELY DO NOT, make a lawnmower blade to where it'll cut you?
   Take the dullest knife you can find in your kitchen drawer. Sling it around at 3600 rpm, and see how dull it is? But more importantly, understand, when you sharpen a blade "down" to razor-edge sharpness, the only thing you're doing is assuring the very second you start hitting the grass, you'll be chipping away at that nice sharp edge, and it'll be worse than it was prior to sharpening it before you get 100 feet into the yard?
   I KNOW, my wife and I have been sharpening people's and our own, for decades. Sharpening them in such a way, is simply a mockery of the design of these rotary style mowers/blades. Also understand, on a rotary engine mower, the outer 1/4"-1" does, 99 percent of the cutting of grass. If you bring that outer edge down to where it'll cut you, you'll assure your blades will be un-sharpenable and shaped like a carrot by the third time around.
   5) Unbeknownst to the average lawnmower consumer, being "educated" on filters, off-season maintenance, location of and checking of minor components, is in fact, the job of the seller. But even if their people in the garden centers are untrained and completely ignorant on these issues, it's the consumers' responsibility to bring that to the store managers attention - because it IS, part of their contract with the manufacturers. Mechanics and service centers will take time to help some people. 6) So, having started, ran and sold two lawn and garden service centers over the course of a life time, being repeatedly certified by every major and many minor manufacturer(s), I feel comfortable in proclaiming, the above response is pure silliness, and the ancient "lie" of, "draining the fuel" that's been sold to consumers for decades, is absolutely, a money-making hoax to literally stir up business, and believe me, it's been the best money-making scandal we ever un-wanting-ly, innocently took part in.

But I'll end responding to this hoax, The ONLY time this would be good, is if, the consumer ALSO, fogged the intake and engine internal components, and indeed some consumers do this, but it wouldn't reach 1 percent of consumer lawnmower users who would even know how, much less take the time to do so.
Therefore, the SECOND and easiest off-season habit to get into is, keeping the tank as full as it can be, (2 or 4 stroke) and then start each piece of equipment every month, run it long enough to flush a carburetors'-worth of volume of gas through it, then, cap off the tank to the top again.

Finally, Consider this: If, throughout the year, (or since whenever the system was taken completely apart, and cleaned out) - that, by the time the end of the year arrives, and you decide to "drain" the system by running it dry, what's going to happen to every drop of water, bad fuel, and foreign particulates etc., that have accumulated up in any one or more of a dozen places inside the fuel system? That's right, it'll be forced to be sucked right up into the carb and engine - just like watching the last ounce of water scurry down a drainpipe. Do Not Do That!

Answer 3

For REAL? Briggs and Stratton are probably the absolute top for these engines and design for landscape 2 stroke machines.

I don't care what anyone says what may be different between brands but winterizing our 2 stroke engines is critical for the health of the machine. Dumping dirty gas out is critical. Blowing the last bit of gas out for the winter allowing the engine to be starved of gas is good for the carburetor. That is what the mechanics I have worked with stand behind.

Water in gas is a very bad thing for the motor. Dirt is just as bad if not worse. Those of us who LOVE our machines would never ever use gasoline with ethanol! The best oil mix with precise measuring! Always changing out the filters. Keep the dirt and sludge (ethanol) out of your machine/equipment will make it last forever.

Obviously you've got carburetor problems; the mixing of gas/oil and air. Something is not tuned correctly. If I were you I would take my B & S mower to an excellent, reputable repair place and get to know these guys!

Hang out! Butter them up! They will love showing off their skills. They will show you how to change out filters, what to check for before dragging your equipment to them to be fixed. Act dumb. Make them think they will not lose your service and that you will (of course) turn your neighbors and friends on to their services. They are wonderful. Haven't met anyone that works in this capacity to not be extremely helpful. Course I am a gal and that always helps but still. They love someone to see and understand what it is they do. They've almost TOO much to fix to deal with and keep customers happy... Fuel, air filters, being able to change these simple filters, use the appropriate NON ETHANOL fuel, measure perfectly the oil/gas mixture..they will become your best friends and viseversa.

Do you know how to test your spark plug? How to fix it to last until the next NEW spark plug? How to fix your pull cord? These guys, you kiss ass and they will show all of this to you!

Whatever the design, the basics are the same: No ethanol, change out filters before necessary, extra spark plugs. Sharp sharp blades! Get extra blades to change out while you are able to sharpen the old or have them sharpened. You touch a truly well sharpened blade you will cut your finger! Sharp blades are critical for the health of your grass. And the look.

Ask them how to keep your undercarriage clean from debris buildup. I used silicone spray, not WD40 which actually absorbs water...keep those machines free of all dirt and they will last forever. The last time I use my equipment for the season I allow the motor to run until it is out of gas. Using only clean gas!

Weed wackers get into a bit more detail with length and weight of line and spin. But your mower relies on the same basics. Is it hydraulic? How high are you able to cut grass? I sure hope you are able to set it high enough to leave 3 full inches of grass. Otherwise, talk to your new buddies about custom raising your deck! Never mow lower than 3" of cool season grass lawns. Warm season is vastly different. Where again do your live?