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Stock Needle?

Discussion in 'Motorcycle Tech Talk' started by JohnnyBiker, Oct 14, 2011.

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  1. JohnnyBiker

    JohnnyBiker Well-Known Member

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    A 3/32 bit fits in that vacuum port hole just right. Look at thread First Dyno Pull Ever started by me and it I have attached AFR info form my runs. I have a set of SE 55cc Sportster heads but I have not modified those as of yet. My bike was originally an 883, now a 1250 and the eyar is 1996. I am not sure about the spring, that looks to not have been messed with, but this is the first time that I have taken one of these things apart by myself so I am not sure what the tell tale signs are. As far as the kit goes for the adjustable needle, it is not a dyno jet kit as I told my indy that I will not accept those parts. Yes he did tell me that I have to change the emulsion tube, but I did not inquire about the compatibility of the stock jets with the kit...
    JohnnyBiker, Oct 15, 2011
    #21
  3. JohnnyBiker

    JohnnyBiker Well-Known Member

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    Here is a response that I got off a different forum that I subscribe to. Does everyone agree here??

    Contrary to popular opinion, the needle meters fuel through a fixed diameter needle jet (and not the main jet. It only passes through the main jet) and there is only one size needle jet for the CV 40 carb. If you're running an N65C needle with a large pilot you may become too rich in the transition form idle. Take a look at what size pilot jet you have.

    I am sure HRK will agree with at least part of this....
    JohnnyBiker, Oct 16, 2011
    #22
  4. Lucifer

    Lucifer Well-Known Member

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    If the needle was from a '90 bagger it's the N72R,Cali baggers had the N72Y...FXR's and Softails had the N72S and Cali models had the N72M
    N72S might be an option for JB because the carbs that came in have an accelerator pump and not as fat off idle as the N65C
    To really fine tune the carb you'd need a selection of the stock Harley needles...but an adjustable needle would probably be quicker and easier maybe just not quite as fine tuned...
    Lucifer, Oct 16, 2011
    #23
  5. JohnnyBiker

    JohnnyBiker Well-Known Member

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    With the chart that you posted I am sure that we will be able to figure out what it is that I need. I believe my indy, or a t least BP had suggested was a 72. I will get there. Finding that N65c and no shim in the carb just changed our course of action. NOw I need to find alternatives. I think that I am going to call the shop that I got my HP stuff from in the first place. They drag race bikes and Sportsters so I think that they may be able to help.. TTYL..
    JohnnyBiker, Oct 16, 2011
    #24
  6. Lucifer

    Lucifer Well-Known Member

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    I agree with the running the N65C needle and a large pilot being too fat ...that's why I suggested dropping the pilot down to a 45 with that needle....
    I disagree with there is only one size needle for a CV40,that PDF file I had fun posting should prove that wrong...
    Lucifer, Oct 16, 2011
    #25
  7. JohnnyBiker

    JohnnyBiker Well-Known Member

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    I found some interesting diagrams that I thought would be helpful to those that use a carb, especially a CV. Enjoy...



    Now we all have access to this information...

    Attached Files:

    JohnnyBiker, Oct 18, 2011
    #26
  8. JohnnyBiker

    JohnnyBiker Well-Known Member

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    Since I am trying to learn what it is happening with my carb, I thought it necessary to do a little bit of research on how the CV carb operates. I found an interesting site that explains the function of the CV in plain english that I think is clear and is easy to understand.

    I was always under the assumption that your carb was only on the pilot circuit until just after idle. According to the following article this is not true. I was at work today and I was thinking about what it is going on with my bike and thinking to myself if I was asking the correct questions to help me understand my problem more clearly. I have discovered that I was not. Upon coming home and logging on to Bike Talk, I received a PM from a friend and he happened to mention what I have been thinking about all day. How long am I really on pilot circuit? In his PM he stated that you are on the pilot circuit until about 1/4 throttle. I remember hearing this before but for some reason I did not remember that while in other discussions with "FRIENDS" that are interested only in helping me understand and to solve my issues with subpar power. :D

    Anyways, here is an article that I found that I would like to share with everyone and maybe we can put this in a tech forum or something, someplace where we can archive this information for others to view should they have questions..

    Carburator Theory and Tuning
    JohnnyBiker, Oct 18, 2011
    #27
  9. hotroadking

    hotroadking Super Moderator Staff Member

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    Your afr CURVE isn't bad in it's shape
    its just too rich.

    Now that we have more information
    it will make it better to determine whats
    going on vs patching the problem
    hotroadking, Oct 18, 2011
    #28
  10. kenfuzed

    kenfuzed Administrator Staff Member

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    Hey Johnny, the diagrams attached earlier look like Bing carburetos and not the Keihin CV's we have on our Harley's (though similar in thory).

    While that Theory and Tuning article describes the a carburetor's function quite well not all of it relates to the CV carburetor used on Harley's. The CV we have does not have a flat bottom slide and acts as both a metering valve and variable venturi. Also the way the pilot (idle) circuit is designed on these carbs the pilot jets cuts out earlier than 1/4 throttle, while the mixture screw controls the transition between the pilot and intermediate (needle) circuit. As the throttle plate opens and vacuum changes, the slide begins to lift. Combined with the pressure drop within the venturi, fuel is drawn up through the emulsion which mixes air and fuel and sprays out the needle jet around the needle. The higher the slide lifts the needle the more a/f mixture becomes added to the air being drawn in through the intake. The slide constantly changes the shape of the venturi and meters the amount of fuel delivered based on the needs of the engine rather than the twist of the throttle, hence Constant Velocity.

    The whole thing is a constant balancing act; mixture screw meters amount of A/F mixture between idle and off-idle transitions, slide meters venturi size at the same time metering fuel spray amount and duration until reaching 3/4 throttle, and the main jet takes over delivery of maximum fuel once the needle has lifted to the point of no longer being useful. In between all of these steps the accelerator pump delivers an extra manual burst of fuel spray to compensate for sudden throttle regardless of vacuum or other conditions.

    All in all the pilot jet keeps the bike idling however having enough idle fuel mixture in that split second of opening the throttle is key to a smooth transition.

    There is a fringe school of thought out there that removing the accelerator pump and relying on the needle and pilot circuit is more efficient. Such methods take careful tuning of the needle by way of shims and requires either a lot of trial and error or a dyno. I've done it, but I don't personally recommend it. Also about 20 years ago I experimented with an adjustable accelerator pump that used a needle screw to set the amount of fuel you wanted delivered. Results were all over the place and I moved on, but years later the same thing suddenly popped up under another name as an accessory for off road use on CV carbs... hmmm coincidence maybe?

    Anyway, determining at what point in the circuit your A/F is going too rich will determine what needs to be adjusted.
    kenfuzed, Oct 18, 2011
    #29
  11. hotroadking

    hotroadking Super Moderator Staff Member

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    Ken fwiu he is rich right from the start
    In the 11's iirc the goes super rich midway 7's the leans out




    Sent from my iPhone using Tapatalk
    hotroadking, Oct 18, 2011
    #30
  12. kenfuzed

    kenfuzed Administrator Staff Member

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    I would be curious to see the a/f chart to see where it's going rich.


    Sent from my iPhone using Tapatalk
    kenfuzed, Oct 19, 2011
    #31
  13. JohnnyBiker

    JohnnyBiker Well-Known Member

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    Go to thread "My First Dyno Pull Ever!!!" graphs are the first, then the afr chart is the second post that I attached something to it....
    JohnnyBiker, Oct 19, 2011
    #32
  14. Lucifer

    Lucifer Well-Known Member

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    Lucifer, Oct 19, 2011
    #33
  15. JohnnyBiker

    JohnnyBiker Well-Known Member

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    JohnnyBiker, Oct 19, 2011
    #34
  16. hotroadking

    hotroadking Super Moderator Staff Member

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    Ken here is the PDF, don't know why it just can't be attached vs telling you to go here and look for it :gah:

    Check the AFR Column, starts at 11.63 and dives down to 9.653 at lowest (so I didn't recall correctly LOL) then climbs back up as the engine demands more
    fuel and doesn't cross into the 14's until 5700

    Even at 5700 it's lean but it's 14.6 which is stoich, which is perfect burn.

    Whenever you got WOT you'll get a curve where it goes leaner as RPM gains
    which is fine, you dont' ride at WOT all day and only there for short periods
    so leaner (this isn't massive leaness) is not bad.

    Attached Files:

    hotroadking, Oct 19, 2011
    #35
  17. hotroadking

    hotroadking Super Moderator Staff Member

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    JB call that Indy ask him to print out a normal dyno run HP/TQ over RPM not time.

    Ask him what dyno he has, and what model (IE Dynojet 250i)
    is the software up to date
    did he use the weather software for correction?
    is he running them STD or SAE

    We need a good standard Dyno print out that we can use,
    these you have over time are not really standard and it's
    why HTT deleted your dyno post as it doesn't meet
    dyno standards. Maybe he (indy) likes it, which is fine
    but for comparison we need the correct print out in SAE
    hotroadking, Oct 19, 2011
    #36
  18. JohnnyBiker

    JohnnyBiker Well-Known Member

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    I got my carb cleaned up today a long with my garage. The parts that I have purchased for my bike is an N65c needle that I thought that I had, a new slide spring, a 45 pilot and main jets sizes 190-200. I will get this nailed. My carb was more dirty than what I have ever seen it...:mad:
    JohnnyBiker, Oct 19, 2011
    #37
  19. hotroadking

    hotroadking Super Moderator Staff Member

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    JB when you first joined wasn't your bike barely getting
    70 or 80 miles a tank? Seems like that the tuning has been the issue
    from day one.
    hotroadking, Oct 19, 2011
    #38
  20. JohnnyBiker

    JohnnyBiker Well-Known Member

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    When i first got my bike I was getting really bad gas mileage that is true, but I am attributing that to just a poor engine set up. I had no baffles, running stock heads, big pipes, high compression, an idiot who shaved my heads on me when I didn't ask him to.. :banghead: And yea I had a bad carb set up as well. I guess I have just had some really bad luck, however, my bike runs well, I am just not getting its full potential. I left if alone this summer just so I could asses the bike instead of changing everything and then not having any idea what what affected what. I haven't bought a single thing really for my bike this past season. My trip to Wisconsin with Red Rider was the starting point for when I started to suspect that something was way off.
    JohnnyBiker, Oct 19, 2011
    #39
  21. JohnnyBiker

    JohnnyBiker Well-Known Member

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    Nozzle question

    Here is something that I am really curious about. When your accel pump is engaged and there is gas getting squirted into the carb, what is the stream of gas supposed to look like? Is it supposed to look like a mist or a steady stream of fuel about 3/32 in diameter?
    JohnnyBiker, Oct 20, 2011
    #40
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