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B&S will not start

I have a B&S model 31Q777. Engine will turn over but will not start. I've checked spark at the plug (good), Put in fresh fuel, checked fuel system, cleaned carb very good, checked woodruff key on flywheel, checked valve clearance, checked push rods, done compression check (90 PSI). I'm the third mechanic in this shop to work on this mower and i would love to be the one to fix it.

Posted by brandon on


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Curtis Sewell

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  • Briggs & Str... Master
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Hi civichatch

Posted on Apr 25, 2013


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Hans Pearson

  • 2510 Answers

SOURCE: Toro, 21" inch push mower

If the engine compression is too low, it will have problems starting or not start at all, and these seem to be the symptoms you are describing. An easy test is to pour some oil into the cylinder and see if that increases the compression. If this makes a difference, you will need to replace the piston rings and at least hone the cylinder, depending on the wear in the cylinder bore.
You can also try spraying some easy start into the intake and seeing if that makes the machine run for just a short spurt. If it does, you could have a problem with the carb not supplying fuel due to something like a blocked jet or irt in passages etc.

Posted on Jun 18, 2011



  • 1 Answer

SOURCE: Cleaned the Briggs & Stratton Riding Lawn

It looks like that your valves need to be maintenanced. This can be done by small engine repair shops. They should have the proper tools.

Also the "timing" of the spark and the fuel injection could be a problem. I hope this helped you.

Greetings Joe

Posted on Sep 30, 2009


Wade Mobley

  • 513 Answers

SOURCE: 5.0 H.P Craftsman lawn more won't start I clean

check gaskets under primer bulb cover

Posted on Jun 28, 2010


Roy Cagle

  • 1545 Answers

SOURCE: AH520 Tecumseh engine will not start; no spark to

I would recommend a serious carburetor cleaning or even installing a new rebuild kit after the machine setting up for so long. The spark problem must be checked for either the (magneto to flywheel air gap) or the condition of the electrical points and condensor on it (if this older model has them)

Posted on Sep 20, 2010

mike butler

  • 6468 Answers

SOURCE: This mower will start but not smooth could armature magneto bee the problem???

check the valve adjustment if overhead valves

Posted on May 29, 2012

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