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Tips to Tuning the Carburetor (1)

Back in the early 1970s, I was working in Southern California and getting pretty burned out tuning stock Harley carbs. So were other hard-core H-D engine builders in the area.

How did Harley carburetors progress from their primitive beginnings to the state-of-the-art CV design they use now?

I know the answer because I played a role in the process.


Back in the early 1970s, I was working in Southern California and getting pretty burned out tuning stock Harley carbs. So were other hard-core H-D engine builders in the area.

Some of us decided to look for a cheap replacement. A couple of guys went out to a foreign car boneyard and picked up two SU carbs from an old British sedan.


The SU carb, made in England, was an advanced design for its day. In the 70s they were readily available in sizes from about 1¾” to 2”, depending on what kind of British rust-bucket you scavenged them from.


The tricky part was tuning the things. This carburetor was unique in that it was designed to meter the fuel and the air simultaneously by using a piston and needle with the standard manually operated butterfly. This design is now known as theconstant velocity (CV) carburetor, and it’s used on motorcycles almost universally.


But it wasn’t back then.

It took a couple of years of trial and error testing but we finally got the tuning of these SUs right for Harley-Davidsons. Gradually the word spread from the tuners to the dealers and manufacturers, who talked to their connections, until . . . SU in England announced a CV carburetor especially for the Harley-Davidson motorcycle!


Their CV carb looked a hell of a lot like the ones we developed, and when properly tuned gave more horsepower and better gas mileage with no transitional flat spots. Just like ours!


About 20 years later the H-D factory figured it was about time to put a CV on their new models. When I see one I think to myself, “Thanks, pals. Nice work, Perry.”

Later came electronic fuel injection (EFI) and another new tuning challenge.

The solution to H-D’s early EFI is laid out in the May 1997 issue of Hot Bike Magazine. I am proud to say that FLO Headworks played the leading role in that project, too.


And since that date we have managed to pick up another seven horsepower with an otherwise stock displacement 80 C. I. engine with 8:1 compression, using my blueprinted CV Keihin carbs and 700cfm air filter kit.


So far SU haven’t sent me any checks, and I haven’t got any thank-you letters from the engineers at H-D either. But my customers are happyFind Article, and that’s been the most important thing for me over the past 25 years.


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Olivia Tong is the freelance writer for e-commerce website and offers the buyers around the world to find quality and discount auto parts. We try our best to aggregate leads in the business world, and let these leads benefit the entire business person.

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