Backfire???

Discussion in 'Lawn Mowing' started by Vibe Ray, May 23, 2001.

  1. Vibe Ray

    Vibe Ray LawnSite Senior Member
    Posts: 785

    What causes a backfire? Is there anyway to stop it? Does it mean something is wrong? My HP usually backfires? Dazzle me with your expertise!!!!
     
  2. Richard Martin

    Richard Martin LawnSite Fanatic
    Posts: 14,700

    Dazzle us with some symptoms. A backfire is usually caused when a fuel-air mixture builds up in the muffler and then a heat source causes mixture to ignite. A backfire can also be caused by the air-fuel mixture inside the cylinder igniting when the exhaust valve is open. Does it backfire when you shut it off or when you are running the engine?
     
  3. 65hoss

    65hoss LawnSite Fanatic
    Posts: 6,360

    Very very common on the kawis. Especially when new. Mine was sounding like a shotgun blast. After all the fuel problems going into the crankcase I shut off all fuel now. I turn the fuel off on the HP and let it run out. This does 2 things. 1st, it allows the motor to cool down before shutoff. 2nd, it doesn't backfire when it finally runs out. I have noticed that by doing this, it has caused the backfiring to stop when I shut it down more quickly.

    If you look into the carb when it is shut off, the kawis have fuel sitting in the bottom of the carb.
     
  4. AB Lawn Care

    AB Lawn Care LawnSite Senior Member
    from Ontario
    Posts: 585

    Just like Richard said...any excess gas that has made its way from the cylinder to the exuast.Once the gas hits the red hot muffler it will light up and BANG!Sometimes this is caused by the carb running too rich.It is common on alot of small engines.My 14 kohler backfires ALOT when it is started.....if you don't start it right.Kohler's are well known for that.Now if it is doing it while running you will need to fix it.
     
  5. mdb landscaping

    mdb landscaping LawnSite Silver Member
    Posts: 2,205

    i have the 25 kohler on my lazer. it will back fire if i dont turn it off properly. i asked the dealer, and the best thing to do is idle the machine down and let it sit for a few minutes and then turn it off. maybe the kawis are different, but since then my machine hasnt backfired
     
  6. cos

    cos LawnSite Addict
    Posts: 1,253

    I back fire too. After eating a couple of tacos at taco bell. I need to sit idle for awhile before I start up.
     
  7. 65hoss

    65hoss LawnSite Fanatic
    Posts: 6,360

    With the kawis, it doesn't matter how long you let it sit before shutting it off. They will backfire. As it breaks in more it will stop. But shutting the fuel off and let it stop on its own works great.
     
  8. Vibe Ray

    Vibe Ray LawnSite Senior Member
    Posts: 785

    I'm sorry I did not mention that it only happens when I shut it off and it is a 19 HP Kawi. Does that help?
     
  9. Vibe Ray

    Vibe Ray LawnSite Senior Member
    Posts: 785

    I'll try out the gas shutoff trick, but doesn't that make it a b*tch to start back up again? And is it completely safe for the engine (no additional wear, etc.)? And why is it more common to new engines???
     
  10. Scraper

    Scraper LawnSite Bronze Member
    Posts: 1,656

    Do you idle down before your cut-off the engine or do you shut it off at full rpm? Try letting it idle for 10-15 seconds before you turn it off.
     

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