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  1. #1
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    Default S&S L Carb Cough on Panhead

    I have an MGL on my (I think) 74" panhead, B grind cam with short drag pipes, bird deflector without air filter. I went from 72, to 74, to 76 on the main and I am still getting coughs as I get up to shifting RPMs and on the freeway. I have not found any leaks using brake clean around the manifold. Would it be uncommon to go 78-80 on the main for this setup or am I chasing the wrong problem?

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    Easy enough to half choke(enrich) and see if more fuel helps at your target rpm.
    Air bleeds are mostly overlooked whilst tuning a carb...
    Advance weights can be tuned too.. Or curves if electronic
    Throw a thunder jet in the mix if you're a glutton for swapping jets

    Seen more than one dist cover screws keeping wieghts fromt hrowing out

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    I have been down this road. ( no success ) w/ my fl knucklehead. Stock air bleed should be .40 and is generally left alone for most applications ( though I'm leaning towards this being my problem). With a velocity stack set-up your main jets need to be about 3 jet sizes up from a carb . With an air cleaner. That being said on my knuckle w/ an air cleaner I played w/ all sorts of intermediate and main combos and always had a bog when the carb was shifting between the intermediate and main jets. Bike started better than any other carb and ran great through the intermediate jet. I have the S&S instructions for this carb and will post them later if you need me to.
    Tim

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    So it sounds like you're having reverberation. This is a common problem with drag pipes, and why we only recommend drag pipes for drag racing, and not for street. Especially with having a large cam grind, your valves are staying open longer, and allowing that exhaust right back into the cylinder, and right back out the carb, causing the coughing.

    Ideally, we're going to tell you to throw an air cleaner on, and baffle your drag pipes. Now.. I know that's not the answer you really want to hear, so here's the next best options:

    Go with a .60 air bleed. This should help a LOT.

    Second, baffles in your pipes, OR.. the "garage" method - about 1" in from the end of the pipe, drill a hole and insert a bolt - find one that goes most or all of the way across the pipe, til it touches the inside of the other side. This acts as a baffle and helps break up some of the reverberation. This was actually a method our racers and mechanics noted works, although it's not the best method, it should help considerably.

    On the bird deflector note, filtration is REALLY helpful. Consider adding some type of filter element.. we are actually working on velocity stacks with a filter element, they should be coming out in the near future.


    From our E/G instructions, found on the website: (same goes for any carb!)

    S&S has found that certain cams and exhaust systems cause poor
    performance at a specific rpm, and attempts to correct problem with carb
    tuning usually degrade carburetion at other rpm ranges. A combination
    of cam overlap, reversion, and back pressure, or even lack of back
    pressure, can cause mixture dilution at certain rpm. This will result in loss
    of power, engine roughness, or misfiring.
    • Drag pipes – S&S does not recommend the use of straight drag pipes for
    street applications. They typically display a characteristic dip in midrange
    performance, and make tuning more difficult.

    https://www.sscycle.com/docs/default...).pdf?sfvrsn=4

    and as always, we offer free tech advice over the phone (866.244.2673) and on the website in a live chat. (We try to keep an eye on forums to chime in, too, but we miss threads sometimes!)

    -S&S

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    Default S&S Cycle Hoorah

    I just read this insert/comment from S&S, I must applaud their involvement.
    Attached Thumbnails Attached Thumbnails A125 (1).jpg   zz (131).jpg  

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    Thanks! We try to get involved in the forums as much as we can, but that's nearly a full time job in itself!

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    Awesome to hear advice from you S&S, would the air bleed jet available for the Super E be the same for the MGL?

    EDIT - From the S&S website:

    "Since 2004 S&S shorty carbs have been fitted with an adjustable main jet air bleed (#13). Changing this jet to a larger size will delay the signal to the main jet, therefore aiding with high speed tuning as described in step 8. This also aides with tuning an engine that is fitted with an exhaust system that is not intended for high performance. The air bleed uses main jets, the stock size is 40. If it needs to be changed the range is normally 50 to 60."

    Does not answer if they will fit in the MGL, but I did have a hard time finding "Air Bleed Jets" because they just use main jets.
    Last edited by FredoSNR; 02-20-2017 at 5:09 PM.

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    Quote Originally Posted by FredoSNR View Post
    Awesome to hear advice from you S&S, would the air bleed jet available for the Super E be the same for the MGL?
    I believe they are . If not , get a micro chuck and micro drill index and work your way up slowly drilling out your existing air bleed and testing . I would make sure the existing one is .040 first and then go from there.
    Last edited by 47str8leg; 02-17-2017 at 6:44 PM.

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