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Tuning Fuel Mix and performance.

Discussion in 'Bling and Appearance' started by FALCON-LORD, May 23, 2008.

  1. Well over the last 2 little while I have learnt little bits of information on the subject, but fear that I have just enough information to be dangerous…
    How do you make sure it is right?
    What are the symptoms when it isn’t?
    When it’s flooding at idle is easy. It sputters and coughs and carries on, then you give it a fistful and it starts to behave when the revs are up… But is there anything else that also gives these symptoms?
    I went into the bike shop after having the carbies sorted saying it’s still gurgling off the line and not really giving me the punch I expect. And they fix it by leaning it out a little…
    How much? I don’t know? If it was to much what symptoms should I be looking for? (BTW It is still a little gutless but so very responsive now)
    Can any one help me here? And more to the point can any one help me referring to a ZZR250 specifically?

  2. Yeah this is why I am asking...
    I don't want to go into this half cocked and cause issues.
  3. Frankly mate, I dunno what it is that you're asking. Your OP is not one of your better cohesive posts. But, I think you're asking what can happen if the bike is leaned too much? You should notice an increase in normal running temperature. Performance will be effected. It's hard to know just where you're at though, so it's better to make that adjustment on a dyno with it's O2 sensor connected

    As for flooding during idle, the only thing I'm aware that would cause that is a carby with a stuck open float/needle.

    Sounds like you need to get the bike to a decent mechanic. Try High Octane Motorcycles.
  4. Essentially I took the bike to a mechanic because it had crap in the float bowl causing it to run rich at idle.
    When I got it back it would hesitate when I rolled on, and it would be a little “chuggy†in its power application, I took it back and they leaned it out a little. Now it is very responsive (Almost twitchy) but still feels a little low on power.
    So basically I want to know if this is something I can learn to adjust myself or if it is something that I should always put in a mechanics hands. Also is it possible that it has been made to run to lean at the moment (No obvious increased heat but in this weather nothing runs hot)
  5. I'm not sure how crap in the float bowl causes it to run rich.
  6. O.K. crap blocking the needle
  7. Have you located the mixture screws?

    They will be a flat-slotted screw aither on the side or under the carb at the front edge.

    If on the side they will almost inevitably be in front of the slide (on the engine side of the slide). That makes them a fuel-adjusting screw.

    Turning out (anticlockwise - hope you can read an analogue clock!) makes the mixture richer. Turning in makes the mixture leaner.

    Do one carb at a time (I know that sounds obvious, but vic pays me by the word...). Listen for the engine speed to vary. Screw in (lean) until the speed slows or gets rougher, then screw it out slowly until you hear it get smooth again. Keep going until it gets rough on the outward journey.

    Count the turns between these two extremes, and carefully screw back in halfway, or until the engine runs smoothly again.

    If you take 15 minutes to do this the bike will over heat and the mixture will not be set correctly. Important note - go for a ride if it takes more than 10 mins (I would not let the bike idle for more than 5, so there!)

    Go for a ride and see how it performs. Remember that idle mixture really only works over the first 1/8 of throttle opening, although I find that in mikuni vacuum carbs there seems to be more overlap. If it doesn't open up smoothly (slowly, not jerking a handful of throttle) try opening the mixture screw 1/8 turn. If that doesn't help, go an 1/8 back from your original setting (screw it in, this time.)

    Playing won't harm anything.

    If one mixture screw or the other does not seem to have a lot of effect, the carb sync could be out.

    There, that's $25.

    All the best

    Trevor G
  8. Which would make it run lean.
  9. Usually "crap" in the fuel, when it gets to the needle area, will hold the float needle partly open and prevent it sealing off the fuel, thus allowing the carb to flood. = rich.


  10. Another random Netriders triplicate post... ;-)
  11. And another random Netriders triplicate post... ;-)
  12. but who in there right mind would try starting a bike with fuel pissing out the over flow?
  13. Yes it was running rich at Idle
    No it wasn’t pissing fuel out of the overflow
    Yes the Mechanic said it was shit blocking the needle.
    If you have something useful to add instead of just being derisive please feel free
    PS. I would like this to be a constructive thread not an other abusive useless pissing contest. On that note, thanks for your input Trevor G