Jetting help
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Thread: Jetting help

  1. #1

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    Jetting help

    So i bought a 1998 carb blackbird with a full akra pipe a bigbore and gasflowed motor the motor has spun a shell on number 3 so i put a good standard lump in there while i rebuild the big lump
    The carbs have 150 mains standard needles and standard air filter
    If i tape part of the intake (air box scoop) it runs ok ish crosswinds and full throttle cause bogging down
    So i bought a dynojet kit and fitted as per instructions 150 mains needle clip on 3 i took it out and it wouldnt take throttle past a quarter (did with the original needles) and same jet size i then changed to 155 mains and the problem was worse
    Ime thinking the clip needs to be on the 5th groove on the needle as with the bigger jet it was leaner than with the 150,s that suggests to me that the dynojet needles are not allowing enough fuel at clip 3 hence made worse with the larger jet they are also a fair bit thicker than the stock needles at the tip

    Its a streetfighter standard airbox but with ducting ect nrmaly found with fairing

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  3. #2

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    Re: Jetting help

    Does the modded motor have the deflectors in the air box region on either side. Stock carbies DO NOT like direct ariflow across the box ports. It drives the CV's nuts and acts like your stating. Just like they hate anything other than a stock airfilter. It's not so much fueling but balance pressure on the diaphrams.
    Route 191 formerly Route 666 Some say that this section of the
    road has 1100 curves in 95 miles.

  4. #3

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    Thanks for the reply its the same airbox (i didnt ride the big bore motor in anger as was ticking when i got it) but i do think it wap a bit stuttesy i do have a spare so i cut these snorkels down (they have a raised ridge line) i cut along this as a guide so they match and drilled a 30mm hole on the underside and was thinking of blocking the front so it gets air thats more stagnant ive yet to fit them as didnt want to change to many things at once

    There is definiteley worse running with the dj needles either way

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  6. #4

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    No deflectors fitted just the snorkels

  7. #5

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    Re: Jetting help

    Ahh there is your problem. The factory setup uses the deflectors along with the body work to mitigate airflow across the intake ports. Your going to have a lot of trial and error to try and stop the issue. Just move in small steps make one change at a time and make test runs in both directions. You have to think in the form of air or water flow. You need to block any airflow across the ports but allow air to enter as well. Think of it as creating a dead air space. Hope your young and have a lot of hair. Your liable to be grey or thinned by the time you've sorted it. Above all be patient and resist the urge to push it off a cliff. Oh and stay away from explosive devices as well they leave a big mess to clean up lol. Just be patient and methodical and you should be able to figure it out.
    The other option would be flat slides $$ believe Tiger ST mentioned 41 or 44 mm.
    Route 191 formerly Route 666 Some say that this section of the
    road has 1100 curves in 95 miles.


 

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