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Odd sound from the Bandit

Discussion in 'Technical and Troubleshooting Torque' started by Bravus, May 22, 2008.

  1. It might be nothing...

    Just noticed that when I'm cruising along on the Bandit (which has an aftermarket pipe) at around 3k revs, which is what it spends most of its time doing, the engine note has a kind of wa wa wa wa wa effect, just softer and louder - i.e. it doesn't say 'wa', it just goes quiet and then loud repeatedly, fast, a couple of times a second.

    It sounds very similar to the 'beat frequency' noise you sometimes get with the bike when riding besde a car with a loud pipe - that same kind of loud/soft 'shimmering' type sound. (It's damn hard to describe a sound in words!)

    It seems to me as though it's a new thing, but it's possible I've just noticed it now because I've settled into the bike more. The power is fine and there are no other ill effects, but the physics of 'beat frequencies' made me wonder about whether it's something about different sounds coming from one or more of the four cylinders into the 4-into-1 pipe.

    Anyone (maybe especially the other Bandit-bandits) have any experience with this? Coming up to 50k service, and I was thinking of getting a dynotune and carby synch anyway...

  2. Yup, my '96 Bandit used to do it depending upon a whole heap of variables some of the time.

    My '06 didn't use to do it with the stock pipe but it does something similar with the yoshi on...
  3. My gsxr has what I assume to be an intake resonance. it was even worse when I had bodywork on it.

    Maybe that's what your noise is.
  4. Slight flutter as the engine has a rich spot in that rev range :?:
  5. Could be - guess we'll see whether a tune sorts it or whether it's just something to get used to. It could be that giving the K&N a clean might have some effect too.
  6. ...cos I just remembered that the (4 stroke) mower hunts up and down in revs, albeit slower, if the air filter is dirty.
  7. Meh, was just sitting here in front of the comp, bored 'cos the family has all gone out shopping... and realised I planned to clean the air filter and lube and tighten the chain this weekend. Too rainy to ride, sadly... but I can do some maintenance stuff -and see if I can solve this noise issue.
  8. Heh, chickened out. Lubed the chain, decided it didn't need tightening but will need replacing before too long because the variation in tightness across it is massive. Started digging for the air filter, but it was a bit of a case of "oh, now I have to take off the tank - oops, can't do that until I take off the rear fairing/body pieces... mah, will get the mechanic to do it when I take it in for its 50k service in a few weeks".
  9. Sounds normal to me :music:
    If theres no power difference and you getting a carby balance, I think you will find its fine :grin:
  10. That's a quite different effect, because a lawn mower is a governed engine, and depeneding on fuel mixture it will speed up or down before being brought back by the governor to the nominated speed.

    A bike has no such similar device.

    To check what it might be, pull the clutch and see if the noise continues, or change to another gear while maintaining the same road speed. It's probably related to the muffler design, in particular its length and diameter.

    There is a particular frequency of exhaust at which the pressure/sound waves inside the pipe/muffler are reflected and in phase with each other. Changing revs even just a little bit will remove the effect.

    I have heard similar effects on various vehicles including trucks, cars and tractors running less restrictive exhausts. The effect is usually overcome by adding an exhaust resonator(!) which damps the additive effect (by changing the reflections). The resonator is added near the end of the tail pipe.

    On a bike you just fit the baffle which was supplied originally with the muffler.


    Trevor G