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  1. #1
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    Default S&S Super B Mid Range Flat Spot Shovelhead

    I recently picked up a used Super B and wanted to try it out on my bike. It's a kick only stock displacement 74" shovel chopper with points ignition. Timing is good, and seemingly no intake leaks (checked with an unlit propane torch). I had a functioning Super E on the bike but I kinda like how the B's look and how simple they are in and out. Plenty of people hate this carb, but I've seen just as many people stick up for it so I wanted to see if I could make it work. I took it apart, used chem dipped it to get rid of the gunked up old gas, and blew out the passageways with carb cleaner and compressed air. It cleaned up really nice, and I replaced the throttle shaft, butterfly valve, and spring with a S&S kit.

    I'm having the same issue a lot of folks have – relatively hard starts, followed by falling on its face in the mid range then picking back up again closer to 3/4 throttle and up. After adjusting the float height to spec, I have tried probably 5 different jet combinations so far using the S&S baseline of .0295 intermediate and .068 main and working around it. I've read that this flat spot is caused by the transition of the fuel through the intermediate to the main when they are both being activated at the same time causing an overly rich condition which then ideally leans back out as the main jet fully engages. Is this accurate? To try and nail down the issue I tried leaning out both intermediate and main, but the problem got worse if anything. Then I tried the opposite beefing up both jets to the higher side of the recommended range, but the stumble was still very noticeable when riding. I've also read about drilling the air bleed in the side of the carb to delay the onset of the main jet, but I'm not sure I can do that on my own. There has to be a way to tune around it, just curious if anyone running a B on a similar motor can chime in. Thanks!

  2. #2

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    Making the main air bleed larger is the way to get rid of the flat spot, if it's flat rich blubbering in the transition. It's really a pipe problem, and you just have to tune it as best you can for the pipes. Changing from a straight pipe to a pipe set with mufflers will help usually. If you want to see how good it can be, use a set of drag pipes 30 - 32 inches long. (Loud.)

    Drilling out the main air bleed is relatively easy since it is readily accessible. The standard size is .042, and you usually need to go up to maybe .060 for the usual drag pipe/Super B combo. You need a selection of small drill bits, the number set from 1 to 60 will include the sizes you need. And you need a drill holder so you can drill the hole by hand, no power drill here.

    Jim

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    You did not mention throttle shaft bushings in your list of replaced parts. Most Super Bs have throttle shaft holes that are worn out. You can rarely get by with just replacing the shaft. That will lead to hard starting and an off-idle stumble.

    Jim

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    This kit provides increased combustion efficiency, more power (up to 5HP) & awesome throttle response. Power you can feel, first time, every time. Kit comes complete with The Yost Power Tube, spacer, easy installation instructions and full tech support direct from the manufacturer.




    What is Atomization?

    If you need the ultimate in a state of the art high performance fuel systems, then Yost Performance Products is your only choice.
    ****Our Products are available through dealers everywhere****

    There are several benefits when you use the Yost Power Tube.

    1. Produces a very fine mist
    The Yost Power Tubes by design, produce a very fine mist, finer than most production fuel injection systems and can be seen and observed by removing the air cleaner and looking into the carburetor venturi.

    (BE CAREFUL, WE DON'T WANT YOU TO BURN YOUR EYES, NOSE, OR ANYTHING ELSE.) This very fine mist allows the fuel to stay in suspension longer for better control of air and fuel mixtures and can be almost perfectly matched for almost any throttle position.

    2. Mid-Range Power and Horsepower
    One of the Yost Power Tubes greatest benefits is extremely good PART THROTTLE response and MID-RANGE performance. This is the most affordable horsepower gain that money can buy. Typically, there will be an increase of 2-5 horses.

    3. Increased Combustion Efficiency
    The Yost Power Tube provides increased combustion efficiency for a more complete burning of the fuel mixture so that you need less fuel to do the same job. The Yost Power Tube is specifically designed to synchronize the engine demand with the air and fuel requirements. (In other words, this Yost Power Tube gives you the proper amount of fuel at just the right time.)

    4. Smoother Running Engine
    You will have a smoother running engine through the entire range, due in large part to the increased combustion efficiency. There is a greatly reduced possibility of pockets of raw fuel burning randomly.

    5. Detonation
    In your combustion chambers, and again because of greater combustion efficiency, the possibility of detonation is also reduced. We have never ridden in scientifically or atmospherically ideal conditions, so I would still be somewhat conservative with compression ratios and ignition timing.

    6. Reduced Possibility of Part Throttle Lean Spot
    This means that ideally you can use a larger carburetor, bigger ports, and more aggressive camshafts with a reduce possibility of a part throttle lean condition. (smaller fuel particles are easier to move and lift than larger particles) but use some wisdom and remember that if you set up a street engine to DRAG specifications, you may have drivability problems at lower engine speeds.

    7. Shorter Warm-up & Reduced Spark plug Fouling
    Most riders also experience shorter warm-up times and a reduced possibility of spark plug fouling. With increased efficiency, the additives present in gasoline are more completely burned, so much so that it is difficult to leave residue deposit on the spark plugs.

    8. Jetting For Atmospheric Conditions
    Providing that your jetting is fairly close to the atmospheric conditions that you are riding in, your engine will run cooler. This can be checked with a thermometer in your oil bag.

    9. Surges & Flat Spots
    The Yost Power Tube is designed to almost completely eliminate surges and flat spots by controlling air-fuel mixtures more precisely, and provides an almost unbelievably smooth throttle response and carburetor circuit transition.

    10. Easier To Start The Main Fuel Circuit
    With the Yost Power Tube installed, it is much easier to start the main fuel circuit, while needing less manifold vacuum to do so.

    Click image for larger version. 

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    Last edited by Dragstews; 05-19-2020 at 9:15 PM.

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    Quote Originally Posted by JBinNC View Post
    You did not mention throttle shaft bushings in your list of replaced parts. Most Super Bs have throttle shaft holes that are worn out. You can rarely get by with just replacing the shaft. That will lead to hard starting and an off-idle stumble.
    Thanks Jim. I was surprised when I replaced the shaft there was virtually no play at all, in fact it went in a bit tight and then was able to spin smoothly once fully assembled. I would have a hard time believing the throttle shaft holes are part of the issue here.

    I currently have drag pipes on the bike, not super long but not super short. No exhaust leaks at the heads. I'll look into drilling the air bleed. By drill holder do you mean a drill press? I haven't been able to find any other detailed instructions on how this is done online.

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    Thanks Drags. I haven't seen this Power Tube before, have you used one with relative success? They are making it sound like the greatest invention since sliced bread.

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    By drill holder I mean a little round pin vise that you can clamp the drill bit in and turn with your fingers. That is what you want to use when drilling out jets, and the air bleed too.

    Jim

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    [QUOTE=HogsRear;846380]

    Have you used one with relative success?

    Maga .....

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    [QUOTE=Dragstews;846396]
    Quote Originally Posted by HogsRear View Post

    Have you used one with relative success?

    Maga .....
    what?

  10. #10
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    Mega >>>> a world of em ...

    Try one .... I'm sure you'll be more than pleased with the results .... !!

    They left out one thing .. (Improves Fuel Mileage)
    Expect about 20 or 30 more miles out of a tank of gas ...
    Last edited by Dragstews; 05-20-2020 at 12:16 PM.

  11. #11
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    Nothing shows on the outside of the main jet nozzle ... It's all internal ...



    Bird's eye view .. ^^

  12. #12
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    Not having any issues but I believe im gonna try one of these

  13. #13
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    if you want to dump the flat spot put some lolly pops in the pipe, then if you still have flat spot after tuning carb play with air bleed

  14. #14
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    Air Bleed on a "Super-B" .....

    ** Mid-Range Tuning **

    The Air Bleed is an air passage connected to the Main Jet emulsion tube that allow air to mix with fuel before it is pulled into the carb throat ..
    You may have found now that by increasing the low speed jet size, the motor responds better off idle but now has a stutter or hesitation (flat spot) as the rpm rises to a level that recognizes the carb's main jet ..

    All Super-B's are manufactured with a fixed size air bleed passage. By modifying the carb to accept jets will allow you to adjust the main jet air bleed size for more control over the main jet circuit signal timing and fuel volume ..

    Takes drilling, tapping and spot facing to accomplish the install of the air bleed jet ..
    The original air bleed size is .042"; suggested range is .054-.072" .. Use S&S main jets for this application ...

    Click image for larger version. 

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    Bore with a 1/4" drill until you reach the cross drill in carb body. (DO NOT GO PAST CROSS DRILL !!)
    Spot face the area with a 1/2" end mill for mating surface of the jet.
    Use 5/16-24 starter tap in hole and then remove to use a 5/16" bottom tap to finish the job ...

    Click image for larger version. 

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    Last edited by Dragstews; 05-23-2020 at 9:27 AM.

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    Alright I ordered a set of smaller drill bits and will try opening up the main air bleed to .060 – also planning on trying the lollipop in the pipes trick. I'll check back in once I get it together. Thanks!

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    .

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    Quote Originally Posted by HogsRear View Post
    Alright I ordered a set of smaller drill bits and will try opening up the main air bleed to .060 – also planning on trying the lollipop in the pipes trick. I'll check back in once I get it together. Thanks!
    Go up on your air bleed size in increments. Because it is an air jet, a change of .004 - .006 is reasonable. You may not have to go to .060, or you may need to go larger. Just part of tuning.

    Jim

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    Quote Originally Posted by Davestune View Post
    if you want to dump the flat spot put some lolly pops in the pipe, then if you still have flat spot after tuning carb play with air bleed
    This helps quite a bit. You can use an eyelet or thumb turn screw. Thereís even an optimal angle for them that you can dial in on your bike. Iíve found that a 45 degree angle is pretty nice! Iíve done it on every bike with drag pipes.
    Last edited by brooklynbomber; 05-23-2020 at 12:07 PM.

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    Quote Originally Posted by brooklynbomber View Post
    This helps quite a bit. You can use an eyelet or thumb turn screw. There’s even an optimal angle for them that you can dial in on your bike. I’ve found that a 45 degree angle is pretty nice! I’ve done it on every bike with drag pipes.
    I actually made a pair with hardware I had laying around and installed them in some new pipes today. I currently have them at a 90 degree angle in the pipe but maybe I should try tilting them a bit like you say. Click image for larger version. 

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  20. #20

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    I had a flat spot with my sporty and the super E.
    I made an adjustable bleed with an idle needle and some brass rod, and drilled and tapped the carb like you would do for the screw in type jets.
    It worked perfectly, but the spring on the needle isn't quite tight enough, so it sometimes needs readjusting. No problem though, I usually noticeit pretty quick and can hold the throttle with my left hand and reach down with my right hand and dial it right in. IMO the carb is too big for my 900.

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