Carb jetting Qs

Discussion in 'Engine, Fuel and Exhaust' started by poolguy, May 15, 2012.

  1. poolguy

    poolguy Member

    12
    0
    0
    I have a 97 sporty 1200 custom,11,000 miles. straight pipes, stock air cleaner with lots of extra holes drilled in back.New seals at carb and manifold. Rejetted to #48, and turned out mixture screw 2 1/2 turns. Runs pretty good. not real quick responsive,stalls sometimes at a stop. and the plugs NGK D7EA are sooted black with the front plug ceramic clean white. where do I go from here?
     
  2. TQuentin1

    TQuentin1 Well-Known Member Staff Member Moderator

    4,633
    83
    101
  3. fin_676

    fin_676 Experienced Member Staff Member Moderator Contributor

    5,279
    133
    158
    The 48 for a slow jet is perhaps a wee bit too much a 45 would be my choice plug being black and sooty the best way to check plug colour is to do a plug chop bike should be pulling hard pull clutch and kill engine at the same time coast to the side of the road and check the plugs
    However modern fuels may not show on plugs in the same way as the older fuels did
    Doing a plug chop will only show how things are during main jet operation if it is still looking rich then perhaps the slow jet is still too big as it delivers fuel all the time
    check operation of the accelerator jet by removing the air cleaner look in the throat of the carb and snap the throttle open you should see a squirt of fuel being directed down the centre of the throat of the carb

    Brian
     
  4. Bodeen

    Bodeen Well-Known Member Staff Member Moderator Contributor

    4,317
    73
    130
    These guy's have you headed in the right direction. I agree with Fin 48 is probably a wee bit big. Turn the idle mixture screw in and see if it try's to stall or not.
     
  5. poolguy

    poolguy Member

    12
    0
    0
    Thanks for the help. I haven't yet changed main jet. I turn the idle mixtur screw in all the way and it will keep running. No washers under the needle. The acc. pump is working and the vacuum piston works fine and its rubber diaphram is good.....
     
  6. Bodeen

    Bodeen Well-Known Member Staff Member Moderator Contributor

    4,317
    73
    130
    A very important part of the idle mixture adjustment process is to be sure your idle rpm is set correctly. The reason is that you can actually render the slow jet useless if the idle is set to high. If you can close the idle mixture screw to lightly seated with your idle rpm's set correctly. Your slow jet is too big and needs to be decreased.
     
  7. TQuentin1

    TQuentin1 Well-Known Member Staff Member Moderator

    4,633
    83
    101
    Your second second tells the tale. That slow jet is too big. Try a 45 and possibly 46 if you have a real high flow air system. You should NOT be able to turn the mixture screw in all the way without doggin' and even stalling the engine. You might also put a couple of #4 SS washers on the needle.

    TQ
     
  8. poolguy

    poolguy Member

    12
    0
    0
    ok, so I picked up a #45 and 180 jets today, hope to get them in real soon, also picked up some washers too. Does anyone believe in drilling out that vacuum hole? What does that actually do for me?
    Also going by ear as far as idle RPMs, I have no tach.
     
  9. TQuentin1

    TQuentin1 Well-Known Member Staff Member Moderator

    4,633
    83
    101
    Nope. Don't do that. Can make your throttle squirrelly.

    TQ
     
  10. Bodeen

    Bodeen Well-Known Member Staff Member Moderator Contributor

    4,317
    73
    130
    Agreed. Do not drill the slide. You are headed down the path of carb happiness. All drilling it will do for you is make you buy another one at some point.