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#4439011 - 06/22/17 10:16 PM 20" Gas lawn mower runs for 20 min - stalls out
69GTX Offline


Registered: 09/23/15
Posts: 3815
Loc: Connecticut
Today I was cutting the lawn and 20 min into it, while stationary on level ground, it just stopped running, like it ran out of fuel. Tank was 2/3 full though! It did this 2 weeks ago but since it was close to being out of fuel, I figured that was the cause. It also fits with another symptom I've noticed over the past several mows, the mower is not quickly getting up to running rpm once it starts. It barely turns over, then over the next 3-5 seconds it sputters up to speed, then acts fully normal. For the past 2 years this Poulon Pro mower has run fine without any of these symptoms. It's 2 years old now and still on all original parts and filters.

B&S 126 cc engine. No choke. Primer button only. Fuel is about 6 weeks old. Considering I've run this mower fine on 6 month old fuel several times in the past, I don't think it's the fuel. This same fuel was fine 4 weeks ago. Another "issue" is that I'm pretty certain the "control run/start bar" has changed position a bit. It doesn't seem to get any resistance until it's almost fully depressed. It didn't feel like that a month ago. Still, it starts and stops via this lever w/o a problem. I don't think that's related to the stopping issue. Been running a little bit of Techron on every fill up this season to help keep the carb clean.

So what are the MOST often seen causes the would shut down the mower after running perfectly fine for 20-30 min, once it gets hot? It will restart, but only run 1 minute the next time, and 5-20 seconds after that. Here are some things I found on line to check - though I've never had any issue on any of these. Never changed them either, never needed to. Change oil...clean air filter...fresh gas...and go.

Spark plug? Clogged gas cap vent? Too much oil? (no, it's just right) Clogged air filter? (not likely, but I washed it very thoroughly anyways for the next attempt). Carb (air/fuel ratio)? Anything else?

This is a first for me. I've had these little inexpensive gas mowers for 20 yrs and the only failure mode in the past has been hard starting to no starting. Any help would be appreciated. Not a fan of pulling apart the carb as the last time I did that, the mower never even started again.
_________________________
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2001 Lincoln Cont 4.6L DOHC/ 39K mi / QS HM 5w30 / FUG XG2
1999 Camaro SS M6 /19K /Mobil 1 0w40 /Fram UG /GM MTL-ATF
1969 Ply GTX/RRs

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#4439016 - 06/22/17 10:32 PM Re: 20" Gas lawn mower runs for 20 min - stalls out [Re: 69GTX]
Syntheticuser Offline


Registered: 06/11/17
Posts: 147
Loc: Waco, Tx.
I would check the ignition. It may be on the fritz. Getting hot and cutting out on ope says ignition. Maybe change the plug to see if it helps lesson the load on the coil. A new plug gapped has the least resistance and should be easier to fire on a weaker coil. Just a guess on replacing the plug...start cheap

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#4439019 - 06/22/17 10:33 PM Re: 20" Gas lawn mower runs for 20 min - stalls out [Re: 69GTX]
CT8 Offline


Registered: 10/09/14
Posts: 11017
Loc: Idaho
Is there spark when it dies? Can you drain the float bowl?
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#4439024 - 06/22/17 10:39 PM Re: 20" Gas lawn mower runs for 20 min - stalls out [Re: 69GTX]
69GTX Offline


Registered: 09/23/15
Posts: 3815
Loc: Connecticut
I'll check the spark tomorrow/just replace it. I probably have some new Champion car plugs out in the garage from previous cars (reasonably interchangeable?)

I've never needed to change a plug on one of these in 20 yrs. A new plug never made one run any better. Figured they were bullet proof for how little use they get. The electrodes always look good. Only 2 yrs old too. Considering I can instantly restart the mower after it dies....suggests there's ample spark. The sputtering and slow startup rpm might be indicative of a weak spark. Though wouldn't it sputter and hunt and full rpm if that was the case? I have no issue with running rpm being nice and smooth....until it just dies like it ran out of fuel?

Float bowl? Haven't resigned myself to looking at the carb yet. Does that bowl unscrew easily without ripping the carb out of the system? I've played around with the various internals on automobile carbs on 1968-1970 models (muscle car tuning), which were no problem. Not sure why lawn mower carbs didn't work for me.
_________________________
----------------

2001 Lincoln Cont 4.6L DOHC/ 39K mi / QS HM 5w30 / FUG XG2
1999 Camaro SS M6 /19K /Mobil 1 0w40 /Fram UG /GM MTL-ATF
1969 Ply GTX/RRs

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#4439043 - 06/22/17 10:56 PM Re: 20" Gas lawn mower runs for 20 min - stalls out [Re: Syntheticuser]
AMC Offline


Registered: 10/17/10
Posts: 893
Loc: South Eastern, CT
Originally Posted By: Syntheticuser
I would check the ignition. It may be on the fritz. Getting hot and cutting out on ope says ignition. Maybe change the plug to see if it helps lesson the load on the coil. A new plug gapped has the least resistance and should be easier to fire on a weaker coil. Just a guess on replacing the plug...start cheap


I think you are on to something. I had a string trimmer that would do this and it ended up being the spark plug. The owners manual calls for a resistor type spark plug and some dope (me) had installed a non resistor plug that said it was interchangeable. If it you are using a Champion plug, make sure the part number starts with an R. If you are using an NGK plug, make sure it had an R below the NGK logo. Other brands I am not sure how they identify a resistor type spark plug.
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#4439062 - 06/22/17 11:26 PM Re: 20" Gas lawn mower runs for 20 min - stalls out [Re: 69GTX]
WobblyElvis Offline


Registered: 09/23/14
Posts: 1355
Loc: Toronto Canada
Re torque the head bolts, might find the bolts a little lose.

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#4439069 - 06/22/17 11:45 PM Re: 20" Gas lawn mower runs for 20 min - stalls out [Re: WobblyElvis]
69GTX Offline


Registered: 09/23/15
Posts: 3815
Loc: Connecticut
Originally Posted By: WobblyElvis
Re torque the head bolts, might find the bolts a little lose.


Once I find them. I'll give that a shot too. Thanks.

Learned about spark plug "reach" tonight. Never knew that...or what any of these letters/#'s designated. Now I know. Neat.

RC12YC is what would work on my B&S.
_________________________
----------------

2001 Lincoln Cont 4.6L DOHC/ 39K mi / QS HM 5w30 / FUG XG2
1999 Camaro SS M6 /19K /Mobil 1 0w40 /Fram UG /GM MTL-ATF
1969 Ply GTX/RRs

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#4439074 - 06/22/17 11:55 PM Re: 20" Gas lawn mower runs for 20 min - stalls out [Re: 69GTX]
ammolab Offline


Registered: 01/16/06
Posts: 996
Loc: Ruidoso, NM USA
Vent in gas tank cap plugged up.
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#4439083 - 06/23/17 12:14 AM Re: 20" Gas lawn mower runs for 20 min - stalls out [Re: 69GTX]
dwendt44 Offline


Registered: 05/17/06
Posts: 3972
Loc: Central Wisconsin
Car plugs cannot be used in a mower engine. Can be used to test for spark though.

Change the air filter anyway, and the gas filter if it has one.
Does filling up the gas tank fix problem?
_________________________
There's no such thing as:
Too big of a battery,
Too large of a gas tank,
or too loud of a horn,
or too bright headlights.

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#4439132 - 06/23/17 04:52 AM Re: 20" Gas lawn mower runs for 20 min - stalls out [Re: 69GTX]
Lubener Offline


Registered: 01/22/11
Posts: 2577
Loc: N.Ohio
Check for spark immediately when it dies. Maybe magneto is breaking down. Give it a shot of ether and attempt to restart. If all checks out, valve clearance could be out of specs, especially when everything is warm.
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#4439159 - 06/23/17 06:53 AM Re: 20" Gas lawn mower runs for 20 min - stalls out [Re: 69GTX]
Donald Offline


Registered: 03/21/04
Posts: 20469
Loc: Upstate NY
Ignition part getting hot and failing.
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2015 Subaru Forester 2.5 engine/CVT
2015 Ford F250 w/Powerstroke
2016 Subaru Crosstrek CVT (wife's)


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#4439197 - 06/23/17 07:41 AM Re: 20" Gas lawn mower runs for 20 min - stalls out [Re: 69GTX]
9050lx Offline


Registered: 11/07/08
Posts: 118
Loc: FL
Had a Tecumseh carb recently that would run from 5 to 20 or so minutes, with all the bouncing around would stir up crud in the tank, eventually clogging the main jet passages.Finally cleaned the tiny carb orifices correctly and solved the problem.It is an Eager 1 6hp. Its a late 90's Sears mower that runs with great power.Brand new carburetors are being sold on E-bay for cheap these days, cheap enough to buy a spare.

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#4439227 - 06/23/17 08:16 AM Re: 20" Gas lawn mower runs for 20 min - stalls out [Re: 69GTX]
69GTX Offline


Registered: 09/23/15
Posts: 3815
Loc: Connecticut
Thanks for the tips. The answer must be in one of those. Let's hope for one of the easy ones. Today, clean air filter, new spark plug and check/clean/remove vent cap.

A failing magneto? Didn't even know it had one.
_________________________
----------------

2001 Lincoln Cont 4.6L DOHC/ 39K mi / QS HM 5w30 / FUG XG2
1999 Camaro SS M6 /19K /Mobil 1 0w40 /Fram UG /GM MTL-ATF
1969 Ply GTX/RRs

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#4439264 - 06/23/17 09:13 AM Re: 20" Gas lawn mower runs for 20 min - stalls out [Re: dwendt44]
HerrStig Offline


Registered: 08/24/11
Posts: 9560
Loc: Boston, MA
Originally Posted By: dwendt44
Car plugs cannot be used in a mower engine. Can be used to test for spark though.

Change the air filter anyway, and the gas filter if it has one.
Does filling up the gas tank fix problem?
My Honda mower takes the same BP6ES plug my SAAB 900 took.

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#4439269 - 06/23/17 09:19 AM Re: 20" Gas lawn mower runs for 20 min - stalls out [Re: 69GTX]
wayne50 Offline


Registered: 06/03/05
Posts: 78
Loc: alabama
I second ammolab and that's the easiest to check first anyway.

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