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Won’t Idle with Heavy backfiring

Discussion in 'The Garage' started by CaelenHaxton, Dec 18, 2021.

  1. CaelenHaxton

    CaelenHaxton XS400 New Member

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    Elkhart
    The bike is 1978 SOHC with 17k miles. So I removed the cylinder cover to fix a massive oil leak, after I reinstalled it the bike refused to start unless I held the throttle open and when revving it backfires heavily. Could the rocker arms have fallen out of adjustment? Any advice would be appreciated as this bike is my daily. Thank you.
     
  2. Buddha

    Buddha XS400 Addict Top Contributor

    Did you remove the 4 viewer plugs to prove the rockers are sitting on the valve stems?
     
  3. xschris

    xschris XS400 Guru Top Contributor

    I would adjust the valves, check the timing and point gaps then sync the carbs with a manometer. When ever you remove the rocker cover your adjustments could go way off.
     
  4. CaelenHaxton

    CaelenHaxton XS400 New Member

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    0
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    Elkhart
    So I adjusted the valves and now it won’t start unless the throttle is held open a little and when it does start it’ll idle pretty roughly and when trying to rev it bogs down for a few seconds(while backfiring out of the left cylinder) then the rpms will fly up. Could the timing be off? I don’t think removing the rocker cover would have affected that…
     
  5. xschris

    xschris XS400 Guru Top Contributor

    Timing might be off but my guess is you valves are off. It's not hard to mess up an adjustment. A few mistakes are keeping the crank from moving while adjusting or turning the crank back to get the marks to line up. Never let this happen as it puts slack in the timing chain and making your adjustments wrong. Setting the valves on the wrong stroke can also cause this. Lots of threads on this in the forum and in the manual.
     

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