Honda H4518 GX640 Dumping excessive fuel

Discussion in 'Mechanic and Repair' started by action13, Jun 19, 2008.

  1. action13

    action13 LawnSite Member
    Posts: 29

    Honda H4518 GX640 GAAD engine code. This mower is dumping fuel out every place, exhaust, carb throat, every where, pull the plugs it will shoot 8' off the walls. Anyone familiar with these mowers? The fuel pump is just plain over pumping, is there something that regulates the fuel pump? This has a brand new Carb. on it, and now has the same problem as with the old carb. TOO MUCH FUEL being dumped in the cylinders. Any help here will be appreciated.
     
  2. S DIAMOND

    S DIAMOND LawnSite Member
    from South
    Posts: 108

    Do you have the fuel line hooked up to the carburetor vent line by chance?
     
  3. action13

    action13 LawnSite Member
    Posts: 29

    Wish it had been that simple, two different size lines........they are in the correct order.
     
  4. S DIAMOND

    S DIAMOND LawnSite Member
    from South
    Posts: 108

    OK, for clarification, you have the (top) line coming from the 3 leg fuel pump going into the carburetor inlet (closer to the edge) not center? You are right the line diameters are different, but...

    This is vacuum regulated from what I can see, and not adjustable. Removing the pump line and placing it into a container while turning it over will give you an indication of "force," but I don't see it as being that strong.

    You say brand new. You actually ordered a replacement (correct model) for this unit and installed it yourself? Or it is practically new (scrap unit) from a different model.

    New or not, if your atmospheric vent is plugged, carb hooked up wrong, or, the classic, the float is not seating you will flood. Interesting problem...
     
  5. action13

    action13 LawnSite Member
    Posts: 29

    Ok, I own a repair shop, I am small engine authorized. Trust me that the carb is connected correctly. Secondly, When I say a new Carb, I mean a new carb from Honda. It is the correct Carb. And doing the samethings as the old one. This isn't a needle and seat problem. This is a high volume electric fuel pump. There is something in the electrical system that controls and cycles the fuel pump, and it's not, it runs constantly. I am just not familiar with this Honda model and was hoping someone here was.........Tom
     
  6. S DIAMOND

    S DIAMOND LawnSite Member
    from South
    Posts: 108

    Tom, I see my mistake, I'm looking at a GX670 Engine (air cooled), not the GX640 (liquid cooled in-line) and you are right, set up is a little different. I am not familiar with this one either; I don't have this engine on file. Sorry. I believe it is relayed controled.
     
  7. action13

    action13 LawnSite Member
    Posts: 29

    Me too, God only knows where it is and which relay...Know where I can download a service manual, or electrical diagram for this model?...Thanks Tom
     
  8. MowerMedic77

    MowerMedic77 LawnSite Bronze Member
    Posts: 1,164

  9. ckbrownla

    ckbrownla LawnSite Member
    Posts: 3

    Tom,

    Did you find the problem? I have one of the GX640 motors and would like to be prepaired if it should act up in this manner. If I read the electrical drawings correctly, the fuel pump gets it's power from the Combination (Key) Switch as does the CDI unit and Fuel CutOff Valve. Because of this design, it would lead you to suspect that the internal fuel pump pressure bypass was blocked somehow.

    I have not taken our unit apart to look at it and will only when it is acting up. Would really appreciate letting me know what you found so I can add it to our troubleshooting guide for the machine.

    Thanks
    C.
     
  10. action13

    action13 LawnSite Member
    Posts: 29

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