Smoking mower

Discussion in 'Shop Talk' started by Oggie, Jun 14, 2005.

  1. Oggie

    Oggie Waste of bandwidth Supporter

    May 29, 2003
    We have a simple non-propelled walk-behind mower with a 4 horse 4-cycle (oil and gasoline not mixed together) Briggs & Stratton Engine.

    It has a lot of hours on it and is smoking out of the exhaust. To compound the problem, a helper grabbed the wrong can and fueled it with diesel. It wouldn't run on that. I changed the fuel and spark plug and cleaned out the carb. It runs now, but I think the smoke is worse.

    Is there an easy way to reduce the smoke? It's a cheap mower, but it's just the right size for trimming and we'd like to fix it.
  2. Runners

    Runners A real Quack!

    Nov 6, 2003
    Near Callands, Virginia
    ...that's all I needed to hear. Back in the mid '80's I took a B&S factory service course. Yeah, it was really neat seeing engines run full throttle behind a thick glass wall & blow up, throw rods, etc.... This was just when the "Magnetron" Ignition was coming out, they had a nifty little retro-fit for it.

    First place I'd look is the breather element & poppet valve to cure a smoking B&S engine. We took a brand new engine, plugged the breather tube, and it smoked like a chimney, unplugged it (while running) and it stopped smoking in about 20 seconds. We also wedged the poppet valve open to prevent the crankcase from pulling a vacuum - and yup, it almost as bad.

    According to the teacher, MOST of the problems with B&S engines start with a poppet valve caked with gunk, stuck open or plugged shut. When the valve is working correctly, we actually pulled +20 inches of vacuum in the crankcase - which was enough to keep oil from being blown past the rings & valves.

    Just take the two little screws out, clean/rinse it really good so it rattles freely, that's about it... Or, just replace it & the fiber washer.