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Carby needles

Discussion in 'Technical and Troubleshooting Torque' started by ibast, Sep 15, 2005.

  1. I just thought I‘d write a bit about carby needles.

    I’ve been mucking around with mine and it struck me that some people may not appreciate how they influence carb performance.

    Needles regulate the amount of fuel being fed into a carby between 1/8th and 7/8th throttle opening, though they has less influence at the extremes of that range. So you can see they greatly influence carburation in 99.9% of riding circumstances.

    The beauty of them is that they can be adjusted fairly easily. It only takes about 30-45 mins to adjust a 4 cylinder and that’s including tank removal etc. Just remember to take you time, be careful not to drop any bits and be especially careful with the diaphragms. All the bits are pretty small and sensitive to small changes.

    I won’t go into their exact working, for fear of people glazing over in indifference.

    All you need to know is that raising them enriches your mixture and lowering them leans it out.

    Not all needles are adjustable, but most are clip type adjustment, where you put the clip one position lower to raise the needle. Some are screw type adjustment.

    You can still adjust the un-adjustable ones, but only if you wish to raise the needles. You just pack them with small washers.

    A handy indicator of which way to go is how your bike performs just after start up. e.g. if you only warm up for a minute on choke and then the bike rides fine, it may be and indicator that it’s running a bit rich.

    In this case you would be looking at dropping the needles.

    Alternatively, if it takes 20 minutes of riding to settle down, it’s an indicator that it’s running a bit lean.

    In this case you would be looking at raising the needles.

    Keep in mind that each bike is different and this is an indicator only.

    Spark plugs can also indicate mixture, but this issue can be confused by timing and variations in petrol.

    Better to make the adjustment and make a gut call on how the bike feels.

    So there you go, if you have changed your pipe or put a air filter in or you just suspect the factory setting aren’t right, you don’t always need re-jetting or a jet kit. You can get your bike running better on a Saturday morning.
  2. Handy bit of info, confirms my suspicions that my bike is running a little rich. Think I might try replacing the air-filter before I go trying to mess with the carby needles though.
  3. Ditto cept replace the words rich with lean....

    And the word accidently with repeatedly, and the word dog with son....
  4. Fascinating....so if my bike starts without needing the choke at all except when it's REALLY cold, and even then only needs choke for around 20 seconds that means it's running too rich, right???

    It's always been like that and I get great fuel consumption too

    Sorry to needle you, but since you raised the subject, I thought I'd drop in.
  5. Possibly. Honda tend to be a bit rich as standard.

    but, it's more of an indication of which way to go, if you think you have a problem.

    Are your plugs sooty generally?
  6. I don't know, I've never even seen them, I leave all my servicing to Rick. However, the performance has always been excellent, so...maybe I don't have a problem..