Super B Rebuild

Article by Mark Trotta

When an S&S Super B carb is dialed in right, throttle response is crisp and there's no hesitation. The power it offers is the best there is for an old Harley!

Due to the lack of an accelerator pump, the S&S Super B is not as forgiving of improper jetting as the Super E and other carbs. They are not a "snap it open" throttle, and probably won't work well out of the box. The only external adjustment on the B is the idle mixture screw and idle stop screw.

The Super B has undergone a few minor changes since it was introduced back in the 1970's, but it's still a simple, reliable performance carburetor. Re-jetting any carb can be frustrating if you don't get the jets right the first time, but it's worth the time.

When I bought my 1976 Sportster, it came with an older Super B. It was previously on a Harley Big-Twin, and without re-jetting it's really too big for a 1000cc Ironhead. However, with a relatively small 1-7/8" throat, the Super B is very adaptable and easily modified.

On my first ride on the '76 Sportster, I noticed a hesitation, actually a bog, coming off idle. Rolling on the throttle slowly didn't help at all.

First, I checked that the idle mixture and idle speed screws are correctly set. Factory guidelines are as follows:

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Reading Spark Plugs

If you want to check your spark plugs to determine how your carb is running, the best way is to look at them right after a Wide-Open-Throttle run. Then close the throttle, pull in the clutch, and shut the bike off. Coast to a stop in neutral. This is the most accurate way to evaluate spark plugs.

If the color of the insulation around the plug electrode is white, your motor is running lean and needs more fuel.

If the spark plugs are dark-brown or wet, it's running too rich. A light to medium-tan color is ideal.

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Re-Jetting the Super B

The Super B uses two jets.

The intermediate jet controls low rpm operation.

The main jet controls the mid to wide-open-throttle operation.

An overhaul includes carb removal and disassembly, cleaning, checking for play in the throttle plates, changing the jets if needed, and reassembly. No special tools are really needed, but time and patience are required.

Overhaul Kit

An S&S Cycle Super B Master Rebuild Kit gives you everything you need except the jets.

An S&S Cycle Jet Packs Master Jet Pack gives you an assortment of popular jet sizes.

When purchased new, the Super B comes with .072 main and .031 intermediate jet. Mine had been through at least two other owners, and had a .072 main and a .265 intermediate. This was my starting point.

On my carb, I tried three smaller main jets (.66, .68, and .70) and two larger (.280 and .295) intermediate jets.

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Changing Jets

You don't need to remove the carb from the bike to change jets (you can remove them from underneath). But, if you have no history of the carb, you may want to take it off and disassemble it.

Drain The Gas

After the air cleaner was removed, the rubber fuel hose was disconnected and stretched into a funnel, then into a gas jug. After draining, I stuck a bolt in the hose to prevent any residual gas from leaking.

There's probably more gas in the carb than you think. There's a 5/8" drain plug under the float bowl that'll let the gas drain out.

To remove the carburetor, loosen the two bands that hold the carb to the manifold. I left the throttle cable attached and took the right-hand grip off the bike.

Once the carburetor is off, find a tray or pan to set it in.

Take out the four screws holding the float bowl to the body of the carburetor. Remove the bowl and gasket from the carb body.

You may have to scrape off the gasket with a scraper. If you use a razer blade, be careful not to knick the soft aluminum gasket surface.

You now have access to the jets.

The main jet is in the center of the carburetor. Underneath it (in the picture above) is the intermediate jet.

Unscrew the main jet.

Here, I used a large, flat-blade screwdriver to remove the main jet. But if you prefer, S&S makes a special tool for this.

The tool part number is #53-0452 and you can buy one here.

The old jet will have a number on the side that tells you what size it is. Replace with the new jet. It is highly recommended to change one jet at a time.

While you have the Super B apart, check for throttle-shaft play. Also check the float level.

With the new jet installed, button the carb back up using a new float bowl gasket. Reinstall the carburetor back on the bike using a new carb-to-manifold o-ring.

Re-attach gas hose. Remember to attach the hose to the overflow tube fitting and route it towards the back of the engine.

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Road Test

After double-checking to make sure everything is good and tight, start the bike up and take it for a ride.

While riding, notice how it performs at different RPM levels. Throttle response should be crisp with no hesitation.

If the issues weren't cleared up by the new jet, chances are you need to go another step on the jet size.

Replacing jets a 2nd or 3rd time can be done with the carburetor still on the bike, it's just a little more awkward. Again, change one jet at a time, reinstall, and road-test again.

Conclusion

By changing my main jet down two sizes (.72 to .68) and intermediate jet up three sizes (.265 to .295), I got the Super B on my Ironhead dialed in just right (after four jet changes).

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Notes and Misc

If you run Wide-Open-Throttle a lot, you may want to change the fuel valve to a high-flow type. Be aware that some of the chrome aftermarket ones are more restrictive than the stock fuel valves.

Running straight unmuffled drag pipes can cause mid-range stumble on a street bike, and may prevent you from obtaining optimum carburetor performance. By creating just a bit of back-pressure on the exhaust, the mid-range stumble may go away.

I'd been running straight pipes on old Sportsters for many years, and was hesitant to do anything that might disrupt that beautiful Ironhead exhaust note. But apparently by adding a 1/4" nut and bolt placed 6" to 8" up the end of each pipe causes enough turbulence to help reduce stumbling.

After time, the weight of the Super B carb may create leaks at the intake manifold gaskets. Installing a carb bracket is recommended. It's also required if you run your bike at a track.

Install a quality gas filter, such as this mini glass bowl fuel filter from Milwaukee Twins.

And it's equally important to have a good air filter.

Lastly, take pictures during the entire process, so that when life gets in the way, you can reference back to the pictures at a future date.

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Related Articles:

Best Carb For Ironhead

Best Carb For Shovelhead

Prep Motorcycle Gas Tank

Motorcycle Carburetor Problems

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