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Atomizing Fuel: The Dell’Orto Carburetor

October 10, 2011 by Matt

Dell'Orto Dellorto Delorto Carb Carburetor Carburettor Lotus Esprit Turbo

The Dell’Orto carburetor never achieved the popularity it deserved. Imagine a dual-barrel sidedraft carb that flows almost as well as the industry performance standard Weber, but is much more flexible and docile in real-world driving, and you have the Dell’Orto.

So why didn’t it catch on? The consensus seems to be a matter of parts availability. Dell’Orto (sometimes spelled without the apostrophe: “Dellorto”) is a small Italian outfit, and it seems they never really had the financial ambition or production acumen of the better-known Weber, and as a result, parts are more difficult (though not impossible) to come by, in contrast the Weber’s almost Holley-like myriad of configurations and applications.

That said, the Dell’Orto was spec’d for a number of factory (not just aftermarket or racing) applications, among them the twin blow-through turbocharged setup for the first-generation Lotus Esprit Turbo, shown at top. They were also used on several Alfa Romeos, and the carb was always praised for its excellent fuel atomization and efficiency, such as it was. It’s a popular aftermarket carb for applications as diverse as Mazda rotaries, Porsche flat sixes or Nissan L-series engines.

And what makes it so much better-behaved than the temperamental Weber? The main reason is a larger accelerator pump. To cover the lean condition and avoid the potential engine stumble when the throttle is quickly opened, the carb provides a quick shot of fuel via the accelerator pump. Nearly all carbs have them (SUs being a notable exception); however, the Weber’s are proportionately small for the carb, requiring bigger main jets to provide fuel to cover for the transition from coasting/idle to the main circuit. The result is lack of metering precision and efficiency for the Weber compared to the accurate, miserly Dell’Orto, although the Weber’s ultimate fuel delivery potential surpasses its rival, generally-speaking. Given the choice, for the kind of driving I do, I’ll take the Dell’Orto hands down.

Editor’s note: This post is part of an ongoing series highlighting various obsolescent methods of fuel delivery. Read the other installments here:

Filed under: Atomizing Fuel, Technical

3 Comments

  1. Joel says:

    Really fascinating stuff! Beautiful engine, love that crinkle finish paint. Perhaps you might address MFI at some point, one of the segues to modern fuel injection. And I’ve always wondered what the specifics of CIS were. At one time, ’73 I think, Porsche offered the 911 with Webers, CIS, or MFI.

    • Matt says:

      Thanks! Yeah, the early Esprit Turbo is a “unique engineering” fan’s dream come true. Some of it is brilliant; some of it is cheap/lazy; some of it is ancient—but it’s never boring. :)

      I’d love to tackle MFI and CIS at some point (the early Mercedes and Corvette MFI systems would be neat to study). I wanna keep the series focused on carbs for at least the next few installments, though; maybe then I’ll branch off into early FI. :)

  2. Mick von Bornemann says:

    Actually single barrel Dell’Ortos per cylinder are very popular for motorcycles, both aftermarket & OEM. Such as Harley XRs, Duces, classic era MVs & probably the most popular club racing carb in the classic era (before the EFI era)

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