25hp Kawi twin backfires

Discussion in 'Mechanic and Repair' started by CT18fireman, Jul 1, 2008.

  1. CT18fireman

    CT18fireman LawnSite Senior Member
    Posts: 611

    I have a 25 kawi twin vertical. It has about 2000 hours, but has been maintained. It starts and runs great. When I go to shut it down I bring the throttle down then shut the key off as always. Lately though about 3 seconds after shutting off it will pop once. If I let it idle for 2-3 minutes it won't. This has been for about the last week. I checked replaced the filter and prefilter, when the filter was off I tried it a couple times and could not get it to pop, but a new filter did not make a difference after a longer run. Choke is open, and as far as I can tell the throttle is all the way down, though tomorrow I am going to check the idle speed then run it and take the cable off and then shut it down to see what happens.

    Any ideas?
     
  2. MowerMedic77

    MowerMedic77 LawnSite Bronze Member
    Posts: 1,164

    How many valve adjustments has it had? Kawi recommends every 300hrs as part of normal maint.

    This has been covered on this board LOTS but one more time can't hurt:rolleyes: The new twin engines with fuel shut off solenoids or anti-backfire solenoids whichever you prefer are designed to be shut down at 1/2 to 3/4 throttle not idle. The solenoid shuts off with the key switch before the coils to keep the cylinders from loading up with fuel and detonating(backfire)

    Hope this helps:)
     
  3. CT18fireman

    CT18fireman LawnSite Senior Member
    Posts: 611

    Its hasn't been done every 300 hours, but 4-500. I just adjusted them less then 100 hours ago.

    This is an 03 I think. Dealer and manual never said anything about where to have the throttle when shutting down and I never have had a problem until last week. I will try shutting it at half throttle.
     
  4. 02DURAMAX

    02DURAMAX LawnSite Gold Member
    Posts: 3,804

    Just let it idle for a bit..like you said 1-2Min my New honda 18hp does the same thing if i dont let it idle..
     
  5. khouse

    khouse LawnSite Bronze Member
    Posts: 1,465

    Try shutting down the engine at full throttle. Make sure there is no holes or leaks in the muffler.
     
  6. 02DURAMAX

    02DURAMAX LawnSite Gold Member
    Posts: 3,804

    That sure as He!! wont help!
     
  7. khouse

    khouse LawnSite Bronze Member
    Posts: 1,465

    O2,
    Tell me why it won't help? Maybe he should try shutting his engine down at full throttle and post his results. Also can you tell me why an engine can backfire if there's a hole in the exhaust? If you can't answer then you need to find out before you say what you said.
     
  8. 02DURAMAX

    02DURAMAX LawnSite Gold Member
    Posts: 3,804

    Cause more unburned fuel stays in the carb.. And them when you start it up it will get a cloud of smoke and i Sure as He!! it will back fire like that!!
     
  9. khouse

    khouse LawnSite Bronze Member
    Posts: 1,465

    Unburned fuel sure does stay in the carb. Because if it's in the carb it can't be fired! So are you saying it backfires at start up? That's how it reads to me. You didn't answer my questions. Problem - If an engine backfires during shutdown. 1. Why does an engine not backfire if shut down at full throttle? Also why can an engine backfire if there is a leak in the exhaust under shut down?
     
  10. CT18fireman

    CT18fireman LawnSite Senior Member
    Posts: 611

    No exhaust leaks. I ran that mower all day today to experiment. At FULL throttle or anywhere above half I could shut it right off and get no backfire. As soon as I dropped it down it would backfire.

    Leaving it at half or more throttle did not cause any startup issues.

    So I guess it did help and thats what we will be doing from now on.
     

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