# [SOLVED] B&S 12.5 hp. starts runs for 2-3 min. then stalls.



## tom99S104x4 (Aug 10, 2009)

hi, i have a 1999 MTD Yard Machine ryding mower with a B&S 12.5 hp. model 28T707-1154-E1.it has a LMT Flo-Jet carb. gravity fed, fixed orifice main jet with adjustable idle jet. the problem started at the end of last summer. i was cutting grass and the engine started losing power sputtering and died. it would not start up again so i let it sit for about half hour and it started right up ran for a couple minuts and started to sputter again and stall. when it starts sputtering it blows out white smoke and if you lower the thottle it helps smoth out the idleling and the white smoke stops but it will still stall in about 30 seconds or so. i checked what ever i could think of and could find nothing so i took of the carb, sprayed it up with carb cleaner and blew out the passages and installed it. the mower was fine for the reast of the season. drained the gas and put it away for the winter. took it out a couple weeks ago changed oil, filters, spark plug, gased it up started right up ran it around alittle everything was fine. today whent to cut grass for first time , started mower whent about 10 feet and it started to sputter and then stalled. same problem starts when you let it sit for awile and idles very well until a couple minuts go by and then sputter, white smoke , stall. i took off carb and cleaned and blew out the passages again but had no efect this time.somone told me it could be the coil but i put a spark tester on the engine and ajusted the gap to almost a half inch and the spark jumped it and started the engine, i wached the spark untill it started sputtering and stalled out and the spark looked strong to me the hole time. so i guess the coil should be good. right now i am leaning toward a carb. rebuild kit but befor i spend 45 bucks i would apreciate any help. Thanks Tom.


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## Basementgeek (Feb 7, 2005)

*Re: B&S 12.5 hp. starts runs for 2-3 min. then stalls.*

I have no real idea on the white smoke on start up other than seals.

Try running with the gas cap very loose. Could be just a clogged vent on the gas cap.

BG


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## luvvgunn (Dec 28, 2005)

*Re: B&S 12.5 hp. starts runs for 2-3 min. then stalls.*

The spark may weaken as the engine warms,tho i would think the best bet would be the carb failing to properly adjust the mix.
New choke springs ,intake filter can go along way to lining a out issues like this.
Another thing you can do/check, use compressed air to blow any debris from under the engine cap,as there is a small blade used to adjust A/F mix,that is moved by the air produced from the rotor's RPM.Check the gap between the magneto and the rotor,as it can aggravate issues . this may help HowStuffWorks "How to Repair Small Engines: Tips and Guidelines"
Good luck and let us know how it goes


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## tom99S104x4 (Aug 10, 2009)

*Re: B&S 12.5 hp. starts runs for 2-3 min. then stalls.*

hi BG, Luvvgunn, i tried the lose gas cap and it made no diff. i pulled the cover off the engine today and checked the gap on the magnito it was within specs, i got out the air hose and blew in ,out and under engine. i did find the spring that is on the choke link had broken off at the very end, so i bent the end and put it on where it belongs. i don't know if it was broken befor i started messing with the carb. or if i broke it when i removed the carb. any ways i started the mower after i put it back together and it ran a little longer then the last times then did the same thing, started to sputter then blue out white or maybe very light grey smoke started to stall, but this time when i lowered the throttle to half position to try and keep it from stalling it did not stall and kept on runnig. after about 15 minuts i mixed up a gallon of gas & seafoam for engines and put it in the gas tank and let in run for about 1/2 hour. then i raised the throttle up a click or two and it kept running so i waited alittle while and did the same thing until it was at full throttle and i let it run for about 15 minuts turned it off and restarted it a few times and it did not try to stall at all. it still idles rough and sputters or it sounds like small back fires. it was raining here all day so i could not take it out and see what happens when i try and cut grass with it. i will let you know what happens tomorrow. thanks guys.


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## luvvgunn (Dec 28, 2005)

*Re: B&S 12.5 hp. starts runs for 2-3 min. then stalls.*

Hello Tom,
White smoke is a result of "rich" fuel mix,the grey tint is from a small amount of oil burning,which is to be expected in older engines.
If SeaFoam made a difference,i would suspect build up in or around the float/ needle valve.
So a compound issue, build up and poor choke control,short of breaking the carb down for cleaning ,replacing springs etc. etc. 
A $2 jimmy rig fix you can try,inline fuel shut off valve between tank/carb,this allows you to adjust it to "starve" the carb countering the rich condition.
A word of warning 1.loose fuel hose clamps can be a very bad thing. 2. running the engine "lean" can cause it to also run hot.
Good luck


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## tom99S104x4 (Aug 10, 2009)

*Re: B&S 12.5 hp. starts runs for 2-3 min. then stalls.*

hi luvvgunn, i ran around like a made man on it today LOL. it ran pretty good today. i cut some grass with it but had to stop do to sinking and getting stuck in the mud , had to push it back to solid ground. all that rain yesterday soaked the ground again. your right about the springs and rebuild kit. i will order them while its running again and have in case it starts up again, otherwise i'll do it in the winter. i'll order an inline shutoff valve to. i was wishing i had one on it while i was working on it . i think after 12 years of beating the hell out of it ,i can invest a couple of bucks in it.i'll run another batch of seafoam threw it to. this is my first post in small engines, i post over in the autoforums. great bunch of people on this site. i was in the middle of installing a valve body in my truck when i got side tracked with the mower. now i can finnish it tomorrow. thanks for your help. LV and BG


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