Bang Under Fierce Acceleration

Discussion in 'Technical Help' started by Old rider, May 26, 2019.

  1. maybe try a colder plug?
     
  2. It was fine before the work to get it running again. Nothing should have changed...
     
  3. hear yah. while i aint entirely convinced myself, its quick and easy to rule out.
     
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  5. You can't mistime the ignition, it's fixed by the ECU map but a duff plug could misfire under load so changing the plugs is worth trying.
     
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  6. That is what, in my inexpert fashion, I meant.

    Not the timing of the signal to ignite but the timing of the actual sparking, due to the physical condition of the plug.
     
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  7. Disconnect the power commander and see how it fairs
     
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  8. Have you changed the belts, all marks line up?
     
  9. Them things can cause all sorts of issues I've heard
     
  10. They can. And take a bit to get off too.
     
  11. Belt change last Summer.
    All was fine until this winter when I was trying all sorts to get it going again after it died in December.
    I’m 95% certain that it’s something I changed or that happened during that period. I went for a longish ride yesterday and it performed flawlessly but I didn’t take it above 7500 rpm or so, it’s at high revs it does it.
    It still goes like stink, even when short-shifting
     
  12. It sounds like the sparks are cutting momentarily. Hence the hesitation and the big bang as the unburnt fuel ignites in the exhaust. I can't remember if you fitted new plugs during the winter but a change of plugs might be where to start.
     
  13. Have you checked belt tension, then. Just to rule out all the easy-to-check things.
     
  14. I initially thought it was sucking in air somehow. :thinkingface:
     
  15. The effects of an air leak in the induction side would be most noticeable at starting, idle and at small throttle openings where the amount of air drawn through a leak is much bigger proportion of the total air going into the engine than at the large throttle openings when accelerating hard. Yet, OR says the bike otherwise is running well.
     
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  16. they also have a distinctive smell when they run lean. especially carbureted models.
    yip, i have sniffed to many exhausts in my time.
     
  17. Maybe the hoses in the gas tank is cracked. Does it occur only when tank is low?
     
  18. No, it happens with a full tank too.
    I did a static test and it happens at about 8500 rpm on minimum throttle to achieve those revs, so not just wide open.
    Have swapped the plug I tried changing during attempts to get it to fire, back for the original one and there’s no difference.
     
  19. i think you should try without the power commander fitted.

    with issues like this, i try to go back to basics and remove as much aftermarket kit as possible ( within reason) to isolate any third party issues
     
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