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20" Gas lawn mower runs for 20 min - stalls out #4439011
06/22/17 10:16 PM
06/22/17 10:16 PM
Joined: Sep 2015
Posts: 3,861
Connecticut
69GTX Offline OP
69GTX  Offline OP
Joined: Sep 2015
Posts: 3,861
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.


----------------

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
Re: 20" Gas lawn mower runs for 20 min - stalls out [Re: 69GTX] #4439016
06/22/17 10:32 PM
06/22/17 10:32 PM
Joined: Jun 2017
Posts: 147
Waco, Tx.
Syntheticuser Offline
Syntheticuser  Offline
Joined: Jun 2017
Posts: 147
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

Re: 20" Gas lawn mower runs for 20 min - stalls out [Re: 69GTX] #4439019
06/22/17 10:33 PM
06/22/17 10:33 PM
Joined: Oct 2014
Posts: 11,816
Idaho
CT8 Offline
CT8  Offline
Joined: Oct 2014
Posts: 11,816
Idaho
Is there spark when it dies? Can you drain the float bowl?


"Don't let your preconceived notions get in the way of facts."
Geoff Metcalf
Re: 20" Gas lawn mower runs for 20 min - stalls out [Re: 69GTX] #4439024
06/22/17 10:39 PM
06/22/17 10:39 PM
Joined: Sep 2015
Posts: 3,861
Connecticut
69GTX Offline OP
69GTX  Offline OP
Joined: Sep 2015
Posts: 3,861
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
Re: 20" Gas lawn mower runs for 20 min - stalls out [Re: Syntheticuser] #4439043
06/22/17 10:56 PM
06/22/17 10:56 PM
Joined: Oct 2010
Posts: 930
South Eastern, CT
AMC Offline
AMC  Offline
Joined: Oct 2010
Posts: 930
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.


18 Honda CR-V - Factory Fill
17 Ram 1500 SLT - Napa Synthetic 5w-20
14 Yamaha Super Tenere - Delvac 15w-40
Re: 20" Gas lawn mower runs for 20 min - stalls out [Re: 69GTX] #4439062
06/22/17 11:26 PM
06/22/17 11:26 PM
Joined: Sep 2014
Posts: 1,446
Toronto Canada
WobblyElvis Online content
WobblyElvis  Online Content
Joined: Sep 2014
Posts: 1,446
Toronto Canada
Re torque the head bolts, might find the bolts a little lose.

Re: 20" Gas lawn mower runs for 20 min - stalls out [Re: WobblyElvis] #4439069
06/22/17 11:45 PM
06/22/17 11:45 PM
Joined: Sep 2015
Posts: 3,861
Connecticut
69GTX Offline OP
69GTX  Offline OP
Joined: Sep 2015
Posts: 3,861
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
Re: 20" Gas lawn mower runs for 20 min - stalls out [Re: 69GTX] #4439074
06/22/17 11:55 PM
06/22/17 11:55 PM
Joined: Jan 2006
Posts: 1,023
Ruidoso, NM USA
ammolab Offline
ammolab  Offline
Joined: Jan 2006
Posts: 1,023
Ruidoso, NM USA
Vent in gas tank cap plugged up.


2009 Honda CR-V
2011 BMW R1200R
2005 Kaw Ninja 250
1994 Jeep Wrangler 2.5L
2016 Chevy SS Sport Sedan
Re: 20" Gas lawn mower runs for 20 min - stalls out [Re: 69GTX] #4439083
06/23/17 12:14 AM
06/23/17 12:14 AM
Joined: May 2006
Posts: 4,010
Central Wisconsin
dwendt44 Offline
dwendt44  Offline
Joined: May 2006
Posts: 4,010
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.
Re: 20" Gas lawn mower runs for 20 min - stalls out [Re: 69GTX] #4439132
06/23/17 04:52 AM
06/23/17 04:52 AM
Joined: Jan 2011
Posts: 2,714
N.Ohio
Lubener Offline
Lubener  Offline
Joined: Jan 2011
Posts: 2,714
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.


The "thinking" man's friend.
Re: 20" Gas lawn mower runs for 20 min - stalls out [Re: 69GTX] #4439159
06/23/17 06:53 AM
06/23/17 06:53 AM
Joined: Mar 2004
Posts: 20,746
Upstate NY
Donald Online content
Donald  Online Content
Joined: Mar 2004
Posts: 20,746
Upstate NY
Ignition part getting hot and failing.


2015 Subaru Forester 2.5 engine/CVT
2015 Ford F250 w/Powerstroke
2016 Subaru Crosstrek CVT (wife's)
Re: 20" Gas lawn mower runs for 20 min - stalls out [Re: 69GTX] #4439197
06/23/17 07:41 AM
06/23/17 07:41 AM
Joined: Nov 2008
Posts: 127
FL
9050lx Offline
9050lx  Offline
Joined: Nov 2008
Posts: 127
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.

Re: 20" Gas lawn mower runs for 20 min - stalls out [Re: 69GTX] #4439227
06/23/17 08:16 AM
06/23/17 08:16 AM
Joined: Sep 2015
Posts: 3,861
Connecticut
69GTX Offline OP
69GTX  Offline OP
Joined: Sep 2015
Posts: 3,861
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
Re: 20" Gas lawn mower runs for 20 min - stalls out [Re: dwendt44] #4439264
06/23/17 09:13 AM
06/23/17 09:13 AM
Joined: Aug 2011
Posts: 9,560
Boston, MA
HerrStig Offline
HerrStig  Offline
Joined: Aug 2011
Posts: 9,560
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.

Re: 20" Gas lawn mower runs for 20 min - stalls out [Re: 69GTX] #4439269
06/23/17 09:19 AM
06/23/17 09:19 AM
Joined: Jun 2005
Posts: 85
alabama
wayne50 Offline
wayne50  Offline
Joined: Jun 2005
Posts: 85
alabama
I second ammolab and that's the easiest to check first anyway.

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