Help with honda 4 hp GX120

Discussion in 'Mechanic and Repair' started by WHIPPLE5.7, Oct 21, 2007.

  1. WHIPPLE5.7

    WHIPPLE5.7 LawnSite Senior Member
    Messages: 958

    This motor just gives a slight backfire noise when pulling over and won't start. I messed with the rocker adjustment somewhat but when I went tighter the popping only got worse and as I backed out it still did it but not as bad. Bottom line is it don't run. I'm thinking maybe the flywheel key broke and turned it out of time. Any other suggestions?
  2. leeker

    leeker LawnSite Member
    Messages: 51

    it could have a valve that is sticking or it could be out of time from a flywheel keyed that is partly sheared. i would check the flwheel key and then do a leak down test . has the engine been seating long. or did it just start doing this
  3. Restrorob

    Restrorob LawnSite Fanatic
    Messages: 11,029

    I would suggest adjusting these valves to spec .004" intake .006" exhaust at TDC compression stroke (both valves closed) and try it again, If still no go do as leeker suggest.
  4. WHIPPLE5.7

    WHIPPLE5.7 LawnSite Senior Member
    Messages: 958

    Thanks guys. I actually just purchased it for my aerator online. The guy said it ran great, but it don't. I can check the key here at home but if it comes to a comp. test I'll have to borrow one.
  5. topsites

    topsites LawnSite Fanatic
    Messages: 21,653

    The first thing I would do is check the oil and make sure it has enough, Hondas are unique because if the oil isn't up to full the engine will not run, all Hondas have a low oil cut off, even their cars. Yes, they'll cut off on you middle of running around too, always check the oil, that's really the only problem I've ever had with Hondas, if you can call it a prob.

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