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    justaguyntn's Avatar
    justaguyntn Posts: 2, Reputation: 1
    New Member
     
    #1

    Jun 16, 2011, 08:35 PM
    18.5 hp Briggs, OHV single cyl Intek Backfire
    I recently acquired a 2004 model Murray rider with the afore mentioned engine.The problem is this, when idleing it runs snooth, advance the power and it backfires through the carb. I checked and changed the flywheel key( had the wrong key installed and was partially sheared), cleaned the carb, changed the plug, re-set coil to flywheel gap. I have been reading here and suspect the valves need adjusting. Anyone with other suggestions?
    crigby's Avatar
    crigby Posts: 4,343, Reputation: 107
    Outdoor Power Equipment Expert
     
    #2

    Jun 17, 2011, 12:42 PM

    Hi,
    You certainly could set the valves to 0.006" per the YouTube videoYouTube - ‪Lawn Mower Repair Valve Adjustment‬‏
    The wise thing is to rotate the engine and watch the rocker arms. They should move about the same. There were a bad batch of camshafts about that time.
    Peace,
    Clarke
    justaguyntn's Avatar
    justaguyntn Posts: 2, Reputation: 1
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    #3

    Jun 19, 2011, 01:12 PM
    Comment on crigby's post
    Thank you Clarke. So if I understand you correctly, excess valve lash can cause backfire through the carb?
    crigby's Avatar
    crigby Posts: 4,343, Reputation: 107
    Outdoor Power Equipment Expert
     
    #4

    Jun 19, 2011, 05:12 PM

    Hi,
    No the bad cam is more likely to do it because the exhaust lobe wears down and you get normal intake and reduced exhaust so that air/gas mix enters and but cannot leave well.
    Peace,
    Clarke

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