Best Carb For Ironhead
Article by Mark Trotta
There's a half dozen or so carburetors that will bolt onto your Ironhead and perform well, but which one suits your bike and your wallet best? Here's a review of the most common carburetors you'll find on 1957-1985 Sportsters.
Early Sportsters (1957-1965) were fitted with side-float Linkert DC carbs, which were simple units to diagnose and repair. For those of you who have an early 900cc Sportster, you know it's a rare bird and you'll probably want to keep it stock. If you have the original Linkert carb, leave it in place.
Read: Linkert DC Carburetor Rebuild
The Linkert DC was also found on other Harley-Davidson models, including the 1957-1966 Servi-car, and one-year-only (1966) Shovelhead. But for those who have a later Ironhead, there's better carb choices.
A switch to Tillotson was seen with the 1966 Harley Sportster. Unlike the Linkert it replaced, it had an accelerator pump and featured a hydraulically operated automatic "economizer" circuit.
The Tillotson carb was complex and had many parts, and was not appreciated in its day. Lack of knowledge and poor parts availability tarnished their reputation, but when set up correctly, they are an excellent carburetor. The Tillotson Model HD was original equipment on Ironhead Sportsters until 1971, replaced by the simpler Bendix unit.
Originally fitted on 1972 to early 1976 Sportsters (and some Big-Twins), the Bendix carb is a popular choice for classic motorcycle builders and restorers who still ride their old scoots. They are relatively simple units that easy to tune and cheap to buy.
Read: Bendix Carb Rebuild
The three styles of Bendix Carb made for Harley V-twins are 38mm fixed main jet (factory style), 38mm adjustable main jet, and 40mm adjustable main jet.
The most common of the three Bendix carbs is the 38mm fixed, non-adjustable main jet version. These carbs are designed to replace Harley 27155-72B and use a single cable throttle assembly. Many riders feel they are the best factory carb for Ironhead Sportsters.
The Keihin carbs found on 1976-1985 Sportsters are fixed-venturi units, not to be confused with the later slide-type (CV) carbs found on 1988 and up Evo Sportsters. The first two years of Keihin-equipped Sportsters had issues (early 1976-1977), but these were addressed and corrected by 1978. In 1979, venturi size went from 38mm to 34mm.
The Mikuni is a slide-type carburetor, also known as a CV (constant velocity) carburetor. Back in the eighties, when I was riding a 1972 XLCH Sportster, other Harley riders used to mock my 40mm Mikuni because it was Japanese. But to my delight and their surprise, the bike started consistently on the 1st or 2nd kick.
Shop: Mikuni Round Slide Carburetor
On an otherwise stock motor, the 38mm Mikuni would be a better choice than a 40mm. Also note that a Mikuni sticks out from the motor more than the stock Bendix, and may give a slight obstruction to your right knee.
S&S Super E
When introduced in 1975, the S&S Super B was the carb to run. That was until the Super E came out in 1990, basically a Super B but with an accelerator pump. The Super E has a relatively small 1-7/8" bore, which allows greater air velocity, resulting in better low and mid-range response for everyday street riding.
Shop: S-S Cycle Super E Carb Only
Shop: S-S Cycle Super E Carb Kit
NOTE: The Super E carb requires the use of a dual cable throttle, one push and one pull.
Push-Pull Throttle Cable
Starting in 1981, Sportsters had a double (push-pull) accelerator cable. This was to help prevent accidental throttle sticking. If your bike is not equipped with one, a dual throttle cable is necessary to install the Super E.
S&S Super B
Although the Super E has gone on to become the best selling performance carburetor in the V-twin aftermarket, many riders still prefer the B over the E model, claiming it has better flow and more low end punch.
I ran a Super B carb on a 1976 XLH, and the difference between the stock Bendix carb vs the Super B was night and day. It's not as forgiving to improper jetting as E carb, but it's my personal favorite carb for a 1000cc Ironhead. Since it wasn't designed to run on a "small" V-twin, careful jetting is crucial.
Read: Tuning The S&S Super B
SU Carb For Harley
The SU was one of the first commonly available constant velocity "CV" carbs, and was a popular carb swap for Harley Panheads and Shovelheads in the sixties and seventies. These variable-venturi carbs were originally found on European cars, such as Triumph, MG, Volvo, and others.
Measured by bore size, common SU carbs are the HS2 (1.25"), HS4 (1.5"), and HS6 (1.75"). For a 1,000cc Ironhead, look for one with a 1.25" bore.
Because many classic cars were fitted with SU carbs, air filters are still available. You could also modify existing air filters to fit the odd 4-bolt pattern on the SU carb. This involves measuring and drilling holes in the backing plate.
Carburetor to Intake Seals
The carburetor on an Ironhead Sportster vibrates quite a bit while running, which may lead to cracked intake seals, vacuum leaks, and rough running.
Replace the carb to intake seals if in any doubt.
A carburetor support bracket is a good idea on any Sportster motor.
You can buy a carb bracket, but they're fairly easy to make if you have a good solid vice and a drill press. The one in the picture above and below was made from a metal shelf bracket.
There's not too much more impressive than a dual-throat Weber sticking off your bike, but these carburetors are very time-consuming to dial in, simply because there's so many variable factors, and one adjustment usually affects others.
Adjustable items on dual-throat carbs include main venturi size, main jet, idle jet, air corrector jet, accelerator pump jet, emulsion tube, fuel inlet valve, and air horns. A dual-throat carb on a Sportster may cause interference with the rider's right knee.
The Mikuni-Solex pictured above is an automotive-type carburetor, but is gravity-fed like most motorcycle carbs. This one came off a modified 1972 Sportster.
In 1984, Harley-Davidson offered the XR-1000 Sportster, which featured a pair of 36mm Dell'Orto carburetors. With several other factory engine mods, power output was 70-horsepower. Weighing in at 490 pounds, the XR-1000 could hit 125 mph right off the showroom floor.
For the money, a 38mm Mikuni is a good choice for 1000cc Ironheads that are stock or slightly modified. But if you have the cash, the S&S Super B or Super E will give you more performance, particularly on the top end.
Motorcycle Carburetor Problems
Classic Motorcycle Resources
Fuel System Maintenance
If you have to store your bike for any length of time, untreated fuel may go bad in as little as three months. Longer than that, fuel system draining or cleaning is recommended.