HOnda GX100 backfiring through carb

Discussion in 'Mechanic and Repair' started by frustrated, Apr 30, 2008.

  1. frustrated

    frustrated LawnSite Member
    Messages: 11

    Ok, I"m completely stumped here. I"ve got a Honda GX100 or 140, not really sure which that IF it will run, it only runs on full choke, for about a minute, then just dies, or it'll pop back through the carb body.

    So far, heres what I've done and checked. Compression: somewhere around 150 Fuel system clean as a whistle with fresh fuel, good bright blue spark which leaves me to suspect either ignition timing, or a valve is out of whack.

    Right now, its sitting there in the very back of my shop after me spending roughly 10 hours last night on fiddling with it.

    Also, what is the stock fuel air mixture screw setting?
  2. SLR

    SLR LawnSite Gold Member
    Messages: 3,210

    Sounds carb related. Either main jet(gas),pilot jet(air) or carb float needle has some clog or gunk in them.
  3. frustrated

    frustrated LawnSite Member
    Messages: 11

    Only thing is, I completely cleared the entire carb, and even swapped it with another known clean carb from another machine. still same problem. I know the fuel flow to the carb is great too.

    I MOW ALONE LawnSite Bronze Member
    Messages: 1,961

    did you ever figure out if it was timing issue? i am having the exact same problem right now went through the carb twice and it is clean this aint my first carb cleaning it is clean. but does the exact same thing as yours. or can anyone else help?
  5. Restrorob

    Restrorob LawnSite Fanatic
    Messages: 11,029

    Check valve clearance, Should be .004-.006 on both intake and exhaust......

    I MOW ALONE LawnSite Bronze Member
    Messages: 1,961

    it is now running with full choke only and will run without dying with choke. :confused:
  7. Phil G

    Phil G LawnSite Senior Member
    Messages: 844

    Without wishing to repeat what's been said; it does sound like a fuel problem. Have you removed the fuel pipe from the carb to check flow from fuel tap? These taps do have issues.

    When you have the carb bowl off blast air into the thread where the bowl nut screws in. Clean with a wire from a brass brush.

    Or check for air leaks around inlet/carb. Have you got the plastic mounting block? Remove, clean and check it.

    Good luck. Phil:ukflag:


    I MOW ALONE LawnSite Bronze Member
    Messages: 1,961

    i was thinking the same thing actually that it might just be sucking air. i will have to check for that. i know it sounds that it is a fuel delivery problem but everything is clean every passage has been blown out with air. thanks

    I MOW ALONE LawnSite Bronze Member
    Messages: 1,961

    im baffled by this one i have good flow of fuel take drain screw off bottom of bowl and it flows nicely. took carb off for third time to check the plastic mounting block no cracks or anything. sprayed carb cleaner around the mounting area and it did'nt suck it in and choke it out at all. but will still only run on full choke. this is a g150 how would i adjust governor on this engine? thanks
  10. Den69RS96

    Den69RS96 LawnSite Member
    Messages: 96

    Backfires are caused by lean conditions or incorrect ignition timing, however if it pops back through the carb, you have an ignition problem. I know nothing about honda engines, but I'd start by checking the valve clearenace. Is it possible to check the timing chain or whatever it has to see if it skipped a tooth?

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