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Totally off topic. Lawn mower troubleshooting

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    Totally off topic. Lawn mower troubleshooting

    So, I have been tinkering around on my roommate's riding lawn mower.
    It is a Briggs & Stratton vertical shaft 16 horsepower single cylinder, if that makes any difference.

    I was told that while mowing last summer, the mower backfired, stopped running, and would not restart after that.

    the following are the symptoms

    Will not start

    Good spark

    seems to turn over too fast

    Carb is in good working order and was cleaned

    while cranking, fine mist of fuel is being expelled from carburetor.

    My best conclusion so far is that the intake valve is burned.
    My theory is that fuel and air is being drawn into the combustion
    chamber normally during the intake stroke.

    But as the intake valve closes and the piston comes back up to tdc on the compression stroke, the compressed fuel/air mixture is escaping past the intake valve, through the intake port and back out the carburetor.

    If anyone here has any other conclusion based on the information provided, please feel free to share.

    #2
    Like anything else, take a compression test and compare the numbers to what the specs call for.

    I'd be worried about the seems to turn over too fast... sounds like little to no compression.
    De-stinking Penelope http://thegsresources.com/_forum/sho...d.php?t=179245

    http://www.thegsresources.com/_forum...35#post1625535

    Comment


      #3
      Originally posted by rustybronco View Post
      Like anything else, take a compression test and compare the numbers to what the specs call for.

      I'd be worried about the seems to turn over too fast... sounds like little to no compression.


      Yes it does
      sigpic2002 KLR650 Ugly but fun!
      2001 KLR650 too pretty to get dirty

      Life is a balancing act, enjoy every day, "later" will come sooner than you think. Denying yourself joy now betting you will have health and money to enjoy life later is a bad bet.

      Where I've been Riding


      Comment


        #4
        I agree that it probably has very little or no compression.

        Couldn't the low/no compression problem be caused by a burned valve? If the valves are not sealing properly, there will not be good compression, correct?

        Comment


          #5
          My vote would be for the flywheel woodruff key, either shearing or nearly so.
          sigpicSome of the totally committed probably should be.
          '58 + '63 Vespa 150's' (London, GB/RI, US)
          '67 X6 T20 ('67 Long Beach, Ca.- misty-eyed)
          '71 Kaw. A1-ugh ('71 SF, CA- worked @ Kaw dlr)
          '66 Yam. YL1('72 SF-commuter beater)
          '73 Kaw. S2A-2Xugh ('73 SF-still parts slave)
          '78 GS 750C ('77 SF-old faithful-killed by son)
          '81 KZ 750E ('81 SF-back to Kaw. dlr)
          '81 GS 650G ('08 back to NE&ME- (project)
          '82 GS '82 (2) GS650GZ, L, Middlebury, G current

          Comment


            #6
            Originally posted by recycled64 View Post
            My vote would be for the flywheel woodruff key, either shearing or nearly so.
            care to elaborate?

            Comment


              #7
              STUCK exhaust valve.


              trust me lol

              smack the engine with a BFH.. if you hear a CLUNK then I was right..

              Comment


                #8
                Originally posted by barnbiketom View Post
                STUCK exhaust valve.


                trust me lol

                smack the engine with a BFH.. if you hear a CLUNK then I was right..

                i pulled off the valve cover and and rotated the engine by hand. the valves are moving normally. if the exhaust valve was stuck open, the valve stem would not remain in contact with the rocker arm (except, of course, during valve overlap when the intake and exhaust valves are both fully closed).

                Comment


                  #9
                  Originally posted by Bigred0216 View Post
                  care to elaborate?
                  Lose or damage the key, lose the timing.
                  sigpicSome of the totally committed probably should be.
                  '58 + '63 Vespa 150's' (London, GB/RI, US)
                  '67 X6 T20 ('67 Long Beach, Ca.- misty-eyed)
                  '71 Kaw. A1-ugh ('71 SF, CA- worked @ Kaw dlr)
                  '66 Yam. YL1('72 SF-commuter beater)
                  '73 Kaw. S2A-2Xugh ('73 SF-still parts slave)
                  '78 GS 750C ('77 SF-old faithful-killed by son)
                  '81 KZ 750E ('81 SF-back to Kaw. dlr)
                  '81 GS 650G ('08 back to NE&ME- (project)
                  '82 GS '82 (2) GS650GZ, L, Middlebury, G current

                  Comment


                    #10
                    a sheared key would NOT make it loose compression...

                    Comment


                      #11
                      a sheared key would NOT make it loose compression...

                      you need to take a REAL compression reading with a Gauge.... it 'seems?" to turn over too quickly..


                      lets find out!

                      Comment


                        #12
                        I have not had the pleasure of playing around with small engines before.

                        from what I understand so far, the engine has gear-to-gear timing.
                        So if the woodruff key shears, or partially shears, it will jump timing because there is either nothing driving the camshaft or the camshaft is so far retarded in relation to piston travel that the valves are opening and closing way too late. Am I warm? I guess it would help to understand the theory of operation of this engine before I go trying to repair it lol.
                        Last edited by Guest; 01-19-2013, 07:28 PM.

                        Comment


                          #13
                          If the woodruff key sheers it would still have spark (unless the engine still uses points), but the spark timing would be way off.

                          Logical if someone hit something large enough with the mower blade.
                          De-stinking Penelope http://thegsresources.com/_forum/sho...d.php?t=179245

                          http://www.thegsresources.com/_forum...35#post1625535

                          Comment


                            #14
                            A key usually shears when the blade hits an immovable object. Loss of correct timing but compresson would still be OK. Need to check compression first and see where that goes before I would work on pulling the flywheel.

                            Comment


                              #15
                              We are talking about a riding lawn mower that uses a belt to drive the mower deck, not a push mower that uses the blade as the flywheel. would the belt not slip on the pulley before damaging the key?

                              Comment

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