[Shop-talk] B&S mower engine, surging and dying. Ideas?

[Bob Spidell]

Addendum:  I'm beginning to think this might be a characteristic of 
air-cooled engines (air-cooled engines have larger clearances to begin 
with).  I've never seen/heard a liquid-cooled engine do exactly this 
but, then again, I don't recall any aircraft engines doing it--they have 
dual ignition systems, maybe that makes a difference?--and, if one did, 
I wouldn't fly behind it.

Bob


On 5/20/2019 8:54 PM, Bob Spidell via Shop-talk wrote:
>
> I had a surging problem on an ExMark--really, a tarted-up 
> Toro--zero-turn and they ended up replacing the engine due to worn 
> rings (intake manifold was getting oiled-up).  Don't ask me why, but 
> nothing else--carburetion, spark, etc.--made sense either.  We're 
> talking a rhythmic pulsing, and not sputtering, right?  Worn rings 
> might make the engine's power ebb-and-flow, I suppose.
>
> Bob
>
> On 5/20/2019 8:48 PM, Scott Hall via Shop-talk wrote:
>> This. Sounds like it's running just long enough to get a vacuum on 
>> the fuel tank, then starving for gas. Then sitting until the tank 
>> reaches atmospheric again. Then repeat.
>>
>> On Mon, May 20, 2019, 7:43 PM Pat Horne via Shop-talk 
>> <shop-talk at autox.team.net <mailto:shop-talk at autox.team.net>> wrote:
>>
>>     Try leaving the fuel cap loose to see if that helps.
>>
>>     Will it start up when it dies with starting fluid.
>>
>>     Peace,
>>     Pat
>>
>>     Pat Horne
>>     We support Habitat for Humanity
>>
>>
>>     On May 20, 2019, at 4:57 PM, David Hillman via Shop-talk
>>     <shop-talk at autox.team.net <mailto:shop-talk at autox.team.net>> wrote:
>>
>>
>>       Ok, I'm out of ideas.  Requesting new ones.
>>
>>       I have a Craftsman walk-behind mower with a 163cc Briggs &
>>     Stratton 4-stroke engine ( engine: 104m02-0008-f1 to be precise
>>     ).  It's only 3 or 4 years old, but it will not run.  And it's
>>     starting to piss me off.
>>
>>       It starts normally ( no manual prime or choke, so it takes ~3
>>     pulls but it always has ), and runs fine for less than 5
>>     minutes.  After that, it surges rhythmically and after a minute
>>     or so of that, dies.  Following that, it will not re-start until
>>     allowed to rest for a few minutes.
>>
>>       I have installed a new plug, new air filter, new carburetor,
>>     and new ignitor.  I checked and set the gap on the plug and the
>>     ignitor to spec ( .030" and .006-.014" respectively ).  Has clean
>>     oil, and brand new gas. Fuel screen in the tank is clean, as is
>>     the fuel hose to the carb. Carb bowl has fuel.
>>
>>       What else can be wrong with it?  It seems to be heat-related,
>>     but it has no cooling system.
>>
>>       Thanks.
>>
>>     Obligatory Shop Content: I can't work on anything interesting
>>     until this damn mower runs.
>>
>>
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>
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