And you checked for loss of spark when?

One thing I didn't mention: some black smoke will come out of the exhaust as the engine begins to cut out.

No, I didn't check for loss of spark (don't know how to do that). But doesn't it seem like a fuel problem?

But then, what do I know...

Seems might be best to break one big mountain prob into small hill probs. Might start by finding out if it is loss of fuel, ignition or mech trouble.

Next time it cuts up, quickly pull off engine air breather, spray cuppla shots of rattlecan carb cleaner directly down into carb throat while assistant is cranking engine normally (50% throttle, PTO sw off, clutch fully depressed, sitting in seat). If engine pops or tries to start, fuel delivery prob. If not, ignition or mech prob.
Next, purchase and USE an inline spark plug wire tester (avail from any briggs dealer) to see if you are getting spark WITH plug fully installed. If so, then mechanical problem.

Come back and update us with your findings - there are experts on this forum for each and all of the "small" problems that can help you to get all fixed.
Finally, LOSE that starter fluid (ether) unless you really want to replace that $$$$ Vanguard before it's time. Ether is not good at all for small engines, better for the big boys.(diesels).

BTW, what conditions of machine use/storage caused the fuel line/carb rust that yer dealer had to clean out?

A rusty fuel tank would cause the problems that you are seeing. If there is a constriction in the fuel system, rust flakes will accumulate there until the line is essentially plugged. You could drain the tank, and check for rust with a flashlight. Also, the shop that worked on your tractor might be able to tell you what sort of gunk they found in the fuel system, when they worked on it recently.

It's a Z-turn mower (no clutch). The mower will start... it just cuts out after a few seconds of running. Does that help? Or do I still need to try the carb cleaner?

The mechanic said that since the valve was the only rustable item in the entire fuel system, ethanol had caused the rust.

The fuel tank is plastic, but there could be guck in it from years of adding fuel from gas cans. The shop guy, in speaking to me, didn't mention any gunk in the lines.

It is generally easier to find and fix a fuel system problem than it is to find and fix an intermittent ignition problem. If your engine stops running when it is hot, it could be because some component in the ignition is sensitive to heat. It is possible for an electronic component to work OK when cool, fail when hot, and then resume working after it cools back down. I can't say if that is what is causing your engine to stop running. I would check to make sure that the ignition module is clear of accumulated grass, and that any sheet metal shrouds are clean, and secured in place. If you can successfully mow in cooler weather, that would lead me to suspect a heat sensitive glitch in the electronics.

"It's a Z-turn mower (no clutch). The mower will start... it just cuts out after a few seconds of running. Does that help? Or do I still need to try the carb cleaner? "

Yes. Just follow a normal engine start procedure.

What kind of choking arrangement is on this carburetor?
Is it a separate choke control with its own knob/lever? or is it "built into" the throttle control functions in that choke position is the extreme upper end of the throttle control range?
I ask because the black smoke appearing just before the engine dies is indicative of excess fuel........or of insufficient air volume. If the carb has an auto choke feature, this might be flopping the choke plate closed and thereby "strangling" the engine.
***"The mower will start... it just cuts out after a few seconds of running. Does that help? Or do I still need to try the carb cleaner?"**
Yes, you need to "try" he spray carb cleaner as suggested by rcbe.
Understand that in this case, the spray carb cleaner is being used as an "alternate" source of fuel being fed directly into the engine (and superseding the OEM fuel system).
If you can get the engine to run by giving the carb shots of carb cleaner when t begins to falter, something is wrong with the carb or fuel system.
If the "alternate fuel" does not keep the engine running, then the issue is most likely something causing a loss of ignition spark.
And this does not necessarily mean a defective magneto either. Anything that "normally" kills the spark, such as when you turn off the key switch, or rise off the seat, or invoke some other aspect of the safety interlock system...............could have a defect that is causing spark to fail.
I suppose black smoke could issue from the exhaust momentarily if spark was lost.............after all........the black smoke merely indicates "unburned fuel" in the exhaust stream. Whether it is "unburned" because there s simply too much fuel, too little air, or the loss of spark will require further analysis.

This post was edited by mownie on Sun, Jun 23, 13 at 14:45

Okay. I'll definitely try the carb cleaner.

Your idea on the safety interlock system makes sense, as I have been having trouble with that. Sometimes I have to fiddle with the brake -- flipping it up and down (on and off) -- to get it to start. Perhaps that system is failing, or there's some kind of loose connection.

Oh, and it is a separate, manual, choke control: it has its own lever.

OK, with a separate choke control, not likely that the choke plate is shutting off incoming air.
Concentrate on lost ignition spark.

Two followups: on thinking about it, I don't think it could be the safety interlock. When that's tripped and I try to start it, I get nothing but a 'click'. But with this problem, the engine will (now just) start, run a second or two, then cut off.

Also, ericwi mentioned that I should make sure the ignition module is free of grass. What is the ignition module and how would I recognize it? Would it be listed on an engine parts list perhaps?

*Many* thanks to everyone for your help. Today I guess I'll try to find an "inline spark plug wire tester" (would an Autozone have one?) and some carb cleaner and do some testing with those.

What I referred to as the "ignition module" is called the armature by the manufacturer. The ignition system is based on the magneto design used before 1982. The older magneto ignition had points, that required periodic maintenance. The new ignition has internal electronic components that take the place of mechanical points. The ignition armature is located near the flywheel, hidden from view. An inline spark plug tester would be used to check the ignition system, to avoid replacing a good part without reason. Power for the ignition system is provided by the spinning flywheel, that has an embedded magnet. So it is similar to the older magneto system. It is also called "Magnetron" by the manufacturer.

"*Many* thanks to everyone for your help. Today I guess I'll try to find an "inline spark plug wire tester" (would an Autozone have one?) and some carb cleaner and do some testing with those."
Prolly better to stop by any small engine shop that is an authorized Briggs dealer - they will have those inline spark plug testers. Of course, Autozone will have the rattlecan carb cleaner (NO ether !! ) :).
Let us know results and we can help from there.

The carb cleaner worked very well; started the engine and it even ran for awhile. So I guess it is the fuel system. I siphoned out the gas in there and put more in, siphoning it out again and discarding it. I just want to get any sediment out that I can.

Anything else I should try/look at?

Thanks.

1) Was that + or - one or two "awhiles" on running? My watch is not calibrated for such. Pls elucidate.
2) Looking back at this thread, culprit seems to be one of three things: a: bad (old) fuel lines from tank to carb (replace any/all) b: fuel pump/ fuel filter (replace with new) c: carb (remove, tear down, clean, rebuild using rebuild kit for that carb, re-asm).
3) Personally, if you find ANY evidence of rust/contaminants in that fuel tank, don't waste your time just trying to siphon the fuel out and somehow flush the tank. Remove the tank and take it to a shop that can steam clean it - particularly if rust is detected.
4) replace ALL flexible fuel lines with new. Blow every line out with compressed air before putting together on machine to get rid of crap.
5) Take pixs of carb on engine before removing, so easy to hook back up!!!! Disassemble completely and soak components in liquid carb cleaner overnite, Using small dia brass wire and MAGNIFYING glass, probe each/every orifice in each carb component. Blow each component out with clean compressed air. Rebuild Carb using components as directed from carb rebuild kit. DO NOT re-use any old gaskets. Remount carb to engine and test. USE "before" pixs to verify correct re-assy.
Alll above is a labor of love and patience. If you have neither, blow moths from purse and get ready to dig deep. Good luck.

Thanks, rcbe. Here's what I know.

1) It ran for a couple of minutes; wouldn't run far. I did make it from my barn to my house to work on it, with only one more shot of carb cleaner.
2) I will try a, replacing the hoses (although they look new). The mechanic supposedly removed and cleaned the carb.
3) It's a plastic fuel tank

where is the fuel tank normally located on the tractor - up behind the dash or under the seat ?

definitely items 4 and 5.... focus on them.

Thanks, rcbe. I changed out the hoses. It's running better but still cuts out occasionally. (Last time it cut out I re-started it, then engaged the PTO and the belt broke! $65 later...).

On the carb cleaning, can you tell me more about a "carb rebuild kit"? Is this something I would need to order from the manufacturer/specialized parts store? Would doing this be pretty involved? I kinda like taking stuff apart and fixing it but I'm not terribly experienced yet and haven't done so with a carb.

Thanks again!

Yeah, you'll need to go to a briggs dealer or service shop that carries such and get a carb rebuild kit for that particular carb. - shouldn't be overly expensive. There is usually an decent instruction sheet included and you can always pick up a repair manual from ebay or such.
Doing the work isn't that bad if you take your time, work methodically and clean and keep track of every part. Also take picx of every step - will help you putting all back together. Soak all the carb components overnite in carb cleaner, then using a MAGNIFYING glass, probe EVERY orifice in EVERY component with a small dia stiff brass wire and blow out with compressed air to get absolutely clean. then put all back together with new components from kits. Be sure to use all new gaskets.
Good luck. Take pix of carb on engine before removing so as to know how to rehook it back up to engine.

Id be pissed that I spent $500 bucks in a shop and its not fixed! In reading these threads it seems as though it may be narrowed down to the carb. Me, personally would try to negotiate with the guy who made 500 bucks for not doing anything, and see what you can get in terms of a concession or refund, and pay someone else (reputable, of course) to rebuild the carb. But that's just me.

Thanks, capriow. My feelings exactly.

But it ran today! I replaced the fuel line to the fuel filter and that seems to have done the trick. I had hope because the fuel filter looked like it had much more fuel after I did that. Once I put on the new mower belt, and it coughed and belched a bit, the mower ran the rest of the day just fine. Took me a couple hours to do my ca. 2 1/2 acre lawn and... so far so good. Thanks for all your help. I hope I never have to continue this thread.

fingers crossed, salt over the shoulder, etc. :)

knock on wood :^)

I realize that this is an older thread, but thought that there is some information that might be valuable as I've looked for solutions to problems that archival information has been helpful.
1. Carbs this small [small pilot/main jets, emulsion tubes...] are HIGHLY sensitive to contamination. I have a step-through scooter, Yamaha V-50 that I had to go through the carb several times to get clean. Each time I'd think "I just cleaned that", yet, stuff in the carb/jets was the problem. Maybe taken apart and cleaned 4-5 times before all the junk got cleaned out.
2. B&S recommend that the valves be adjusted yearly. Air cooled engines move [expand/contract] more than liquid cooled engines. VW engines should have valves adjusted every oil change [3,000 miles/5,000 Ks], probably not a bad idea for these as well [yearly/oil change].
3. With seasonal usage, there are a lot of things that can happen over the non-used down time, condensation in the fuel, dead fuel, varnish in the fuel system, rust and corrosion of the fuel system, rust and corrosion of the ignition system. Drain fuel, clean and put up properly, don't just park it.
4. Start with the basics, fuel, fire, compression.
A world of wisdom on this forum, in this thread alone, something like "solve a mountain problem one hill at a time", that's pure gold.

Turns out it was some kind of breather tube that was clogged. I found the right mechanic and he found it right away.

Yank, I wish I could drain the fuel tank. No way to do it on this model. I try to run it until the gas is gone. Oh and I use ethanol-free gas now.

I've been running my 12.5 flatty for a while, then it just seemed to run funny [not idle right as it normally idles well now that the limiter cap has been removed] and powered up slower than normal [still powers up haltingly as it is jetted so lean].
Dumped the float bowl, got some liquid [dirty water] in the bottom. Drained down about a litre out of the tank into a funnel with a rag [filter] into a gas can. All good now. This was less than a teaspoon of sediment that was putting the engine off.
So, little stuff on little engines is big stuff [according to scale].
Glad you got it running.