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backfireing with flames

Discussion in 'The Garage' started by agreen33, Feb 4, 2014.

  1. agreen33

    agreen33 XS400 Member

    I recently straight piped my exhaust. I didnt rejet carbs as I saw no sign of loss of power or any other vital signs. Recently I was reving my engine at night and I noticed when I backfire which happens often since I straight piped I get flames shooting out of my exhaust. I read somewhere that backfireing isnt actually bad for your engine. I guess I just want a second opinion
  2. Sesty

    Sesty H.E. Pennypacker

    I would think flames out the exhaust is a vital sign for a need to rejet... since you changed pipes and have much less back pressure i would retune. You should take a look at you valves and timing as well.
  3. eric123

    eric123 XS400 Addict

    Flames out the pipes sound like it is rich and the unburned fuel is igniting. When pipes or intake is opened up, the mixture usually leans out somewhat though...Your plugs will tell you whether you are rich or lean...
  4. agreen33

    agreen33 XS400 Member

    Would you guys know of a good place to find a rejetting kit?
  5. Sesty

    Sesty H.E. Pennypacker

    are you running stock jets now with OEM intake or did you switch to pods
  6. agreen33

    agreen33 XS400 Member

    I am running stock jets and stock intake I believe
  7. Tombo

    Tombo XS400 Addict

    My guess would be lean from going to a less restricted exhaust. To explain the flames, I'm not sure. Could be that it is just the extra hot flame from combustion lasting till the exhaust valve opens, or perhaps it is that your bike misfires from time to time from fuel starvation and then that fuel ignites due to higher temperature burn from running lean.

    In either case look at your plugs. Pictures and we can advise you

    Posted via Mobile
  8. Sesty

    Sesty H.E. Pennypacker

    would check your plugs, and open up dem carbs. who knows what the Previous Owner did to the carbs, cant hurt to know what your running in there!
  9. agreen33

    agreen33 XS400 Member

    I have been running it like this for about a month is there any other damage I should be aware of othat i might have caused other than I suppose the plugs?
  10. Sesty

    Sesty H.E. Pennypacker

    excess heat from running lean is never ideal, and your plugs could be totally fine. The color of them is what your looking for to help identify if you are running rich or lean. pull them and take some photos
  11. Scorpio1963

    Scorpio1963 XS400 Guru Top Contributor

    mikesxs,Parts n more,bike bandit ,ebay and your local motorcycle shop are all good places to look for jetting kits.As for lean very long it can significant damage to your pistons so I would fix the problem asap.
  12. bcware

    bcware Well-read Top Contributor

    The flames are from the lack of back pressure; it's "normal" or as normal as normal can be when you're running open headers.

    Is the engine backfiring or popping? Loud backfiring would be abnormal, but it should spit and pop a bit; I would expect as much. I also recommend looking at the plugs. Don't let your heavily modified exhaust determine the direction of tuning alone; open headers can be deceiving.
  13. 16VGTIDave

    16VGTIDave XS400 Guru Top Contributor

    What colour are the flames? I'm going to guess blue, which would indicate a lean misfire. A lean mixture, as pointed out, is bad and will lead to engine damage. If the flames are orange, then the mixture is rich. A rich mixture is not good and will cause carbon deposits.
  14. agreen33

    agreen33 XS400 Member

    I believe the flame was mostly blue with a bit of orange.
    Here is the picture of the plugs they both look the same

    Attached Files:

  15. bcware

    bcware Well-read Top Contributor

    What size jets are you running? Have you actually checked the numbers yourself? Your plugs look mixed. They look both too rich and perhaps too lean.

    They appear too rich for stock jets with no mufflers, but parts look burned clean.

    Choking the bike may be causing the rich appearance.

    I would get a fresh set of plugs and run the bike without choking it.

    Stock jets should cause a lean condition without any mufflers.

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