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Another jetting question!

Discussion in 'Technical and Troubleshooting Torque' at netrider.net.au started by deafwish, Jun 9, 2006.

  1. I'm wanting a slip on exhaust for my Hornet 600.
    I already have a K&N air filter in the airbox and still have the standard end can, with the standart carb' jetting.
    I assume that when I fit a race can with the K&N, it will need to be rejetted, right?
    I don't really want to be paying $400 odd on having it rejetted, as all I'm really after is a good exhaust note.
    If I change back to the standard air filter and keep the slip on, will it simply run just like it does now?
    Does this make any sence? Does your brain hurt, too....? :oops:

  2. Any change to the inlet or outlet may cause mixture differences.

    Usually it's a lean out.

    Some bikes run rich right across the range. As such when you do the pipe and filter thing, they come back to the right ratio and thus don't need rejetting.

    Honda's tend to fall into this category.

    Get some Honda specific advise on this, but you may be alright with both changed.

    Be careful, however. There are 3 mixtures you are concerned about and it might be right up high but off in the mid range and at idle.
  3. Its like telling an asthmatic that its ok to smoke.

    The K&N will allow more air into the plenum, the can will allow more air out.

    Get the air and fuel right and the bike will breath much better and exhaust cleaner.

    Get the mixture too far wrong and you could be doing damage.
  4. a bloke at the mech shop told me that you dont need to bother re jetting a 250, if you fit a slip on, the exhaust in question is a staintune. is this true??
  5. I fail to see what difference engine capacity has to do with the equation.

    They all work the same way.

    Try it and see, if it runs like a pile of crap then get it rejetted.
  6. you don't "need to", but even the jetting on a stock bike isn't perfect.

    i'd think he meant it is just more money for minimal performance gain...
  7. I had a Staintune slip on, on my VTR250 and it ran fine.
    I did use the standard air filter though.

    What I really want to know, is can I do the same on my Hornet i.e. Slip on can with standard air filter :?:
  8. the short answer - yes
  9. if the headers are stock then i think there shouldn't be too much problem, and the K&N shouldn't be too much either. only one way to find out though :grin:
  10. Ok, here's the simplest way to do this...
    - Leave the K&N filter in your airbox... it'll help things in the end.
    - Go get whichever pipe you want... whatever flicks your switch.
    - Run it and see how it goes. If it's getting flat spots or starts misbehaving then it's time to establish if it's leaning out or just running like a pig due to the new flow characteristics.

    If it is leaning out, then it might be worth finding out if the stock needles in the Hornet 600 have circlip adjustments or if they're fixed. If they're circlip adjustable then i'd just drop the clip one notch to richen it up across the board slightly. If that fixes it, enjoy! :D If it doesn't then start shopping around for an aftermarket jet kit to suit the bike. If you contact one of the many carb jet kit makers and advise them as to the extent of modification to the bike they'll be able to steer you in the right direction.

    BUT... the job a good tuner (not just a mechanic!!!) who has experience with Hornets will be able to do for you will always be better than simply a circlip-shuffle or a generic 'jet kit'.
  11. i have a zx2r and have an after market air filter and sports muffler and it is running rich. the outlet of my muffler is very black and has thick carbon build up compared to my bros cbr. i keep hearing people rejetting their carbs when they have aftermarket stuff.
    what is involved in rejetting? how does this fix anything?

  12. Some bikes and some pipes need to be rejetted desperately when a slipon
    is fitted. Some do not need it at all. Generally Staintune pipes do not
    require a re-jet. Generally 250s do not require a re-jet. However if the
    carbs are a little bit off anyhow, the pipe might make it worse.

    Keep the K+N filter, fit the pipe, ride it and see if you have a smooth
    powerful supply of power or if it kicks in sudden. See if it rides better
    with the choke on. See if it rides worse when hot. See if it starts
    without the choke when it is cold. Any of these issues need rejetting.

    If you are not sure, pay $50 for a mixture test on a Dyno. You don't
    need those cool graphs with the horsepower on them, you need
    an air vs. fuel graph. Should be about 13 parts air to 1 part fuel, across
    the whole rev range. If your mixture is wrong at one or all RPMs then
    you will know what to adjust (show us the graphs and we'll tell you).

    Rejetting is to pull apart the carbs which mix fuel and air together in the
    right proportions for the engine. Replace the nozzles (jets) with
    different sizes, and maybe adjust or replace the needles too,
    and adjust a few other things, to change the amount
    of fuel supplied to the engine. Reinstall, and ride faster, smoother
    and more economical!
  13. There are 3 mixtures you need to worry about.

    It could be rich in some areas and lean in others.

    Look here for more info


    Product support
    CV carb tuning
    High RPM engines

    Fortunatly on a 250 it's easier to do plug chops. It's a different story trying to get a full throttle plug chop on an 1100
  14. get the bike ran on a dyno before you start worrying to much.
    a lot of bikes dont need any adjustment at all..
    but just to make sure its not leaning out at high rpm
    the dyno is the best bet. all exhaust companys say you should
    check your jetting just in case.
  15. thanks alot for all of your input guys. appreciate it alot and i will go and get it looked at today. from what i can see it that sometimes when looking at the muffler, i see a lil bit of petrol coming out but when riding it hard, no big clouds of black smoke. thank god!
    anyways im off to see the mechanic now and hopefully its just a carb adjustment.

    cheers guys