Briggs 12.5 hp IC fuel problems

Discussion in 'Mechanic and Repair' started by briggerman00, Oct 16, 2007.

  1. briggerman00

    briggerman00 LawnSite Member
    Posts: 10

    Ok guys here is one for you I have a briggs 12.5hp IC engine model#286707, Type#4021-01, code#970204ZB, the problem I am having is I have rebuilt the carb, when I start it it will run at idle kind of rough then when I go to increase the throttle the fuel floods the engine out, I have even changed carbs which is known to be good, and the same thing happens, is my problem a carb problem or is it a fouled plug problem?
    Any help would be greatly appreciated.
    Jeff
    briggerman00@charter.net
     
  2. Bill Kapaun

    Bill Kapaun LawnSite Senior Member
    Posts: 923

    For the cost of 1 spark plug, I'd just go ahead and change it!

    Is it puffing black smoke when it stalls?

    My first guess is that the engine sounds too lean, not too rich.
    Vacuum leaks in the carb mount gaskets or worn throttle shaft.

    Is this the Nikki or Walbro carb?
     
  3. briggerman00

    briggerman00 LawnSite Member
    Posts: 10

    Yes that is what I am saying, replace the plug then proceed on, there is no smoke when it stalls, as I increase the throttle the engine starts to gag on fuel that is being shot into the carb, then it dies because of all the fuel in the carb
     
  4. Restrorob

    Restrorob LawnSite Fanatic
    Posts: 11,023


    Knowing this could be helpful ???
     
  5. briggerman00

    briggerman00 LawnSite Member
    Posts: 10

    Both of the carburetors are Nikki
     
  6. leeker

    leeker LawnSite Member
    Posts: 51

    did this unit run fine before you put a kit in the carb. or what was the reason for the carb rebuild. is this the same problem you had before the carb rebuild?
     
  7. Bill Kapaun

    Bill Kapaun LawnSite Senior Member
    Posts: 923

    I'm still not convinced it's flooding.
    Just for grins, apply the choke to varying degrees and then try accelerating the engine.
    Does it improve or get worse?
     
  8. Restrorob

    Restrorob LawnSite Fanatic
    Posts: 11,023

    I'd be willing to bet a non fully seating intake valve/worn valve guide is causing the fuel to mist out of the carb instead of sucking it in.

    I've seen quite a few mist the fuel back out.

    A compression/leak-down test would show if it is the valve since you have tried a known good carb with the same results.
     
  9. leeker

    leeker LawnSite Member
    Posts: 51

    i would bet that restrorob is on the right track! idles rough and wont throttle up is a good indication of a valve problem.
     
  10. ArchZangel

    ArchZangel LawnSite Member
    from Florida
    Posts: 24

    I have seen the problem with a sheared flywheel key. I'd give that a check too.
     

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