low speed carb re-jet

Discussion in 'Engine, Fuel and Exhaust' started by robertnj63, Aug 1, 2009.

  1. robertnj63

    robertnj63 Member

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    My 2002 dyna defender kept coughing and cutting out whenver cruising at a steady throttle, never when accelarating. The bike only has around 3000 miles and completely stock. I finally took it to the dealer and they replaced the slow jet with stock #27165-90. The bike no longer cuts out now, but it doesnt start easily when warm. It used to fire right up when i just touched the button, now it takes 10 tries to get it to start, and it starts "lazily" when it does. Is there a different technique with this new jet. Previously, i never primed the gas, just hit the button and it lit up. Any ideas?
     
  2. NEWHD74FAN

    NEWHD74FAN Experienced Member Retired Moderators

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    One of the problems with having someone do the work with only ONE minor problem is when finished theycan introduce more problems, (you do not know what peripheral damage they could cause getting to it. The plus side in this case is...you have a warranty associated with the work done. Take it back and find out what they did...likely original cause may have been varnish binding needle/diaphram slide assembly, or when Stage I carb mods were done, they used a drill to "open her up a bit". If you go in the self help section and look under fuel/carb, it will help understand how it works. Changing the low speed jet likely is leaning things out way too much...of course the other thing is, they "diddled" with the idle mixture screw...should only have to adjust it 1 1/2 to 2 turns from "gentle" seating.
     
    Last edited: Aug 1, 2009
  3. robertnj63

    robertnj63 Member

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    Thanks for the response, but

    This carb is factory stock, it didnt have any stage 1 or anything else done to it. From what i understand, the new low speed jet that they put in is actually a "richer" jet. Everything seems to work fine now, except the hard starting when warm. I was just wondering if there is a new technique one has to do with this new low speed jet. A trip back to the dealer is a real pain!!!
    Thank you
     
    Last edited by a moderator: Aug 1, 2009
  4. NEWHD74FAN

    NEWHD74FAN Experienced Member Retired Moderators

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    Factory stock means that it was running fine before...and nothing was changed, then some debris or vacumn leak or internal part failure in the carb has changed...but since the servicer was into it...use your warranty now, otherwise you will void it and you will need to learn carburetion mapping in the self help section to be sure.
     
  5. TQuentin1

    TQuentin1 Well-Known Member Staff Member Moderator

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    That jet number you listed is a #48 jet. That is pretty big and will in fact be rich (if not VERY rich). See here for some very good guidance on jetting the standard Keihin CV-40 carb:

    *Twin Cam CV Carb Rejet Suggestions - Harley Davidson Community

    And to answer your question about starting the bike, NO - there should NOT be a special, super-secret starting method when a carb has been jetted. BTW, the real question here is why the bike developed a problem with the coughing etc over time. 3000 miles is nothing. Just barely broken in. So I would tend to believe there was/is another problem now being masked by the overly rich low jet (like an intake leak, etc.).

    TQ
     
  6. robertnj63

    robertnj63 Member

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    i would assume the dealer would check everything out. from what i read here, some harleys come so lean that they can damage themmselves!! so the low speed jet is too rich??do you know what jet comes with it stock?could this rich jet cause hard warm starting problems0
     
  7. fin_676

    fin_676 Experienced Member Staff Member Moderator Contributor

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    The service manual for your bike will tell you what the stock jetting was
    when accelerating the accelerator pump ads extra gas when you open the throttle
    if original problem was when at a steady speed id suspect the main jet being to small or the needle height being too low
    by fitting a larger slow jet this increases the fuel to the engine throughout the rev range of the engine including at idle
    so may be too much fuel at idle and correct amount at steady throttle
    so reducing the slow jet to a 45 and upping the main by 5 may give better results

    Brian
     
  8. TQuentin1

    TQuentin1 Well-Known Member Staff Member Moderator

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    Like I said above, my concern is that from your description this problem developed over time. That does NOT sound like a jetting problem, but rather something else like an intake leak or something. Putting in a larger slow jet would compensate for this by masking any excess air that is not coming through the venturi. So I would go back to basics and see why the bike started to run poorly. I do not believe the solution should have been a larger jet.

    TQ
     
  9. NEWHD74FAN

    NEWHD74FAN Experienced Member Retired Moderators

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    1+ for TQ, if the bike was stock and running fine, but the problem developed over time, you have to find out what changed. Jetting & mixture changing is masking the symptom or whatever is the "root cause". Try to remember when it started running rough...start of the riding season (did you winterize it), or did you let the old fuel stand in the bowls, all the fluids changed out and Stabil added to your fuel left in the tank? Battery connected to a "Battery Tender". Added a recent accessory or went on a trip and gassed up in an unfamiliar place...plenty of slippery slope items to check, before changing the "factory settings".
     
  10. robertnj63

    robertnj63 Member

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    I have no history on the bike as i bought the bike from a funeral director who used it for traffic control..i got it with 2500 miles on it. I ran 5 tanks of seafoam through it and than had the carb cleaned and it still cut out. After the trip to the dealer it stopped cutting out and now hard starts when warm. Thats all the history i have. The other thing i noticed is it doesnt seem to have the power it had before they switched the low speed jet. I found myself at full throttle when passing cars, etc. I never noticed being at full throttle before. Im not a wrencher so i am at the mercy of the dealer. I am going to print out these suggestions and hopefully they can fix it the proper way.