REF: Carburetor, Intake Manifold & Exhaust

Aftermarket Carburetors Installed on Sportsters 1957 - 2006


Keihin BD (Screaming Eagle 40mm Kit)

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Aftermarket Carburetors and Upgrades

Mikuni Carbs

Sub Documents

HSR Series:

VM Series:



Other than exact replacement OEM carburetors, all Mikuni aftermarket carburetors and tuning components are sold “As Is” for off road / racing use only. 1)
They are not intended or approved for use on vehicles operated on public roads or in locations where applicable engine tampering and anti-pollution laws apply.

Counterfeit Mikuni Alert!!:

There are plenty of Mikuni and Keihin carburetors in the market that are not authentic. 2)
They're not safe to use and will cause many problems to your bike.
If you're not sure if it's a genuine carburetor, the Sudco International site has a web page with pics of genuine and fake carbs.
Follow this link or you can call them directly to verify a seller. 3)

Click on the pic to enlarge.

Mikuni vs CV-40:

Mikuni HSR42 on a relatively low powered bike:
Not a whole lot. Some, but not a lot.5)
Mikuni HSR42
Now let's bump the power up a little bit to see what Mikuni brings to
the party: Still not much. Course, this isn't a whole lot stronger bike. 6)
Mikuni HSR42
OK, now let's put it on a bit stronger bike:
Holy cow, made a pretty big difference at this power level. 7)
Mikuni HSR45
Now let's step it up some more: Shazam.
It's worth nearly 11hp on a 111hp bike! 8)

S&S Carbs

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S&S Super B Series

9) 10)

Throttle shaft leak repair.
Counter-bore each side a few thousandths less than the O-ring thickness so it sits a little proud. 11)
These are 1/4“ x 3/8” O-rings from a HF&T kit.
Then use a couple 1/4“ ID SS washers with a good synthetic grease like Super-Lube.
The return spring is on one side and you position the throttle lever on the other side.
So the washers just pinch the O-rings but still allow proper throttle movement. It should solve a shaft leak problem and can be easily maintained.
This was done on a milling machine with a mold ejection pin that fit perfectly.
To keep center, the pin was put in the spindle collet with an indicator as a confirmation of position after having moved the Z axis.
12) 13) 14)

S&S Super E Series

Accelerator Pump

There are 4 screws to take out to remove the float bowl.
Three obvious ones and the fourth one is one of the accelerator pump screws as in below.

Removing the accelerator pump.
The spring inside holds the diaphragm up until the rod pushes it down like a bellows.
15) 16)

Kmotor Super E (copy?)

This is some of the wording of the advertisement on Ebay. 17)

This carb is billed as “New 11-0420 Carburetor Super E Shorty Carburetor Big Twin or Sportster Carb”.
US $64.97/ea. “1 year warranty. This is a brand new, high quality direct fit OE style replacement part”.
The Super E are butterfly type carbs with fully adjustable idle mixture screws and changeable intermediate and main jets.
The idle mixture screw is positioned and angled for easy accessibility. Even with 5 gallon gas tanks, adjustments are not a problem.
The Super E has a 1-7/8in. (47.6mm) throat at the butterfly and is identified by an E cast into the throttle linkage side of the carb body.
All Super series carburetors use a special enrichment device instead of a choke for starting. This leaves the bore of the carburetor unobstructed for greater air flow.
The Super E enrichment device is activated by a variable position lever attached to the air cleaner backplate.
By simply adjusting the lever, starting and warm-ups are made easy and foolproof.

It's actually made by “Kmotor” out of China if you read the fine print on the bottom of the add.
But the wording in the add makes it sound like the S&S Super E. There is no data suggesting that this isn't a good carburetor.
It may actually be a cheaper alternative.
However, it is something to take into account if your intention is indeed to buy an S&S model.
Here is the carburetor:

Kmotor Super E next to a Keihin butterfly 18) No S&S markings 19)

S&S G, F and L Series

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Rivera SU Carbs

Sub Documents

1970s Era- Lake Injector

Sub Documents

* How to adjust the Lake Injector for all throttle positions

  • Originally made for airplanes, the Lake injector was a popular fuel delivery system in the 70s era. It was designed for the ultimate in performance with a minimum of tuning effort. Don't confuse the word “injector” with fuel injection, as these series of carburetors are not a fuel injector or a fuel injector body20). The body design, plus the velocity stack in unison with the throttle slide, forms a venture which enables the injector to achieve a good fuel/ air mixture. 21)
    • The manufacturer claimed a 15% - 25% or more increase in horsepower, unequalled acceleration, immediate starts and instant tuning.
    • Installation was a simple bolt on design with no modifications needed.
    • Suitable for 883s as well as 1000 model Sportsters although could be installed on Shovels, Pans, Triumphs and Hondas.
    • Body options for an extra price include, show chrome, bright anodized and 24K Gold.
  • A true low head, nil pressure injector as does not depend on venture suction like a carb but just pure air mass flow, so it self corrects for great altitude manifold pressure changes.22)
  • You wont fine tune this nail in a tube, they run rich when the tanks full, and get lean as the fuel drops.23)
  • Many people have to plumb air supply to the tank with a 'pop off' to keep pressure head constant below 1 PSI.24)
  • The unit is gravity feed instead of having a fuel pump for delivery and it was prone to leaking if you left the petcock open.25)
  • Posa and Star are all very similar and found their way from small aircraft and onto bikes.26)
  • POSA, Lake Injector, Revflow and Aero Carb are all float-less, diaphragm-less carburetors.
  • These carbs do not operate well on more than .5 lbs of fuel pressure yes that is less than half a pound of fuel pressure. These carbs do not vent any fuel vapor that may form in the body to the venturi as there is not float bowl well or diaphragm vent.27)

Bendix Stromberg Carburetor Identification

  • Bendix Stromberg used a unique identification scheme where a series of letters and numbers were assembled to identify and describe how a carburetor was constructed. The first two letters described the carburetor design, followed by a number that identified the size, and numbers and letters to identify specific design details and modifications.
  • The first (two) letter(s) comprise a Basic Design Code that places the Bendix Stromberg carburetor in a design category, where:
    • A – Pressure Injection Carburetors
    • E – Pressure Injection Carburetors
    • NA – Float-Type Carburetors
    • P – Pressure Injection Carburetors
    • Q – Pressure Injection Carburetors
    • R – Fuel Injection Systems
    • S – Speed Density Metering Systems
  • Example: NA-R9G
  • Prefix- “NA” – for float-type carburetors followed by a ”-“(dash)
  • The next letter indicates type, where
    • S – Single venturi updraft designed for two, three and four cylinder engines in the 25~95 hp class. NOT fitted with economizer, acceleration pump or mixture controls.
    • R – Single venturi updraft, designed for engines of all types in the 50-400 hp class. All are similar in design and incorporate needle valve type mixture control, accelerator pump and economizer. Some bodies are interchangeable in this series and deferent design economizers are used.
    • D – Double updraft venturi, with the float chamber to the rear, was considered obsolete c.1930
    • U – Double updraft venturi, with the float chamber between barrels. See specific models for details.
    • Y – Double vertical venturi (updraft), with two float chambers fore/aft of barrels. See specific models for details.
    • L – Inverted, down draft venturi.
    • T – Triple venturi, double float chamber fore/aft of barrels. The NA-T4 series is the only known model. Designed for use on Wright J-5 and other 9-cylinder radials, where each venturi feeds three cylinders. It has float similar to Y series, but with back suction mixture control. No economizer or accelerator pump.
    • F – Four-venturi with two separate float chambers. The last letter and numbers indicate a specific model.



The Weber is a very tunable carb for different motors with a nearly infinite set of jets, emulsion tubes, chokes, etc. 32)
The angled manifold that swings the carb towards the front of the bike, giving you leg room to tuck in behind the manifold / carb.


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36) 37) 38)

Sudco International Corp. 2410 S. Sequoia Drive Compton, CA 90220 Tel.(310) 637-8330 • Fax (310) 637-8331
photo by Yellowstone Kelley of the XLFORUM
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