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need help troubleshooting a 12.5hp b&s

ggpr2's Avatar

Join Date: May 2007
Posts: 4

05-26-07, 09:46 AM   #1  
need help troubleshooting a 12.5hp b&s

went to cut the grass today with my bigger mower today for the first time this year and it initially wouldn't start.

Replaced spark plug and it now starts...and sounds like the muffler went

Its a Briggs & Stratton 12.5hp i/c quiet motor in a powerturf mower

It runs okay (somewhat smooth) for about 30 seconds then gets rougher and rougher until it stalls(near stalling point you can feel the tractor jiggle like an off balance washing machine). You get about 40 feet of grass cutting then it gives up.

If I undo the oil cap while running, causes it to stall.
trying to start it with the oil cap undone has it jump up and down 2 inches. (maybe someone put to much oil in last year, or blown head?)

did a compression check and it comes back with 60 psi(I am assuming this is low).
^^having the oil cap on or off doesn't seem to effect the compression ratio.

every time it tries to stall and some-what recovers...a big cloud of smoke comes out (I think its dark, but not 100%).

I don't mind fixing it myself, as everyone has to start somewhere with small motors, but I want to make sure that it requires me to go to that step and I would also prefer to have a rough idea what I would be looking for and what I need when I take it apart (eg, schematic, special parts, etc...).

Looks like I get to use my mothers 8hp to cut the grass today.

thank you.

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ggpr2's Avatar

Join Date: May 2007
Posts: 4

05-26-07, 10:16 AM   #2  
Model: 286707
Type: 0420-01
Code: 91032211

ggpr2's Avatar

Join Date: May 2007
Posts: 4

05-26-07, 11:21 AM   #3  
cleaned gas cap (I think it was clean, but just to make sure)
put carb cleaner through air filter and gas tank, forced it to run for about 30 minutes and then it was good enough to cut the grass, by the time the grass cutting was done, it was running great again.

I still need a muffler (ears ringing) and still curious if the psi is supposed to be 60 (haven't checked it after it started to run good again)

cheese's Avatar
Forum Topic Moderator

Join Date: Jul 2001
Posts: 16,575

05-26-07, 10:42 PM   #4  
It's hard to trust a compression reading on a single cylinder small engine. If it runs good, it has enough compression.

"Who is John Galt?" - Ayn Rand (Atlas Shrugged)

God bless!

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