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| Features |
| Tech Talk: Tom Barth’s Dell’Orto Tuning Tips |
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by Tom Barth
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Editor’s Note: While we will continue on in the coming weeks with the ongoing series of Dell’Orto tech articles by Canadian Bob Hogg, we wanted to also share the knowledge of Tom Barth with Green Flag Motorsports in Waterford, Mich. Barth’s experience and knowledge has been gained from 35 years of racing, maintaining, designing and building competition karts. The last 10 years has been focused on the shifter kart through sales and service to the karting industry. This experience is also backed up by 40 years of automotive product, manufacturing and assembly engineering experience.
Green Flag Motorsports offers additional information on the Dell’Orto Carb through the sales of The Dell’Orto Primer available on his website as well as sales and service of Dell’Orto parts for both ICC and TaG engines. The Michigan-based company is also a dealer for TM, Motori Seven and Pavesi engines in addition to the Birel and Topkart chassis and numerous other product lines. Barth offers rebuilding services and arrive and drive programs in addition to parts sales. For more information on how to order the Dell’Orto Primer or to learn more about his products and services, visit http://www.greenflag.net or call (248) 674-2325.
- RMB
Part 1- Vacuum
Probably tuners today understand more about electronic fuel injection than carburetors. When tuning their new ICC or TAG many become somewhat discouraged when it becomes apparent that there is something amiss and it is no doubt the carburetor. The basics are the same for the carburetors as for EFI (mixing air and fuel for a combustible mixture) but the function of the carburetor sometimes can be confusing when trying to make it work properly.
An understanding of the following three items will make tuning somewhat easier for those that don’t have previous experience with the carburetor:
● The part that vacuum plays in metering fuel
● Air/Fuel ratio
● The four phases of operation
If the tuner understands that the strength of the vacuum plays a key role in correct fuel metering then tuning becomes a little easier. Knowing what the vacuum strength is at the various throttle openings can help in identifying certain problems.
Vacuum is created by air pulled through the carburetor pulling fuel through the idle jet system. - at idle, vacuum is present in the idle circuit. Because the throttle valve is closed or nearly closed, fuel is drawn from the idle rather than the main circuit. More simply, the idle fuel bypasses the main circuit and exits downstream of the main nozzle through the idle port.
Accelerate the engine (a signal for more fuel). The vacuum source is now from the main circuit and is stronger (but not at full main circuit strength) causing fuel to switch direction from the idle port to the progression port.
At this point the progression takes place which is the transition from the idle circuit to the main circuit. This means that fuel that was passing through the idle port downstream of the throttle valve has changed direction (idle port) and is now flowing through the progression port directly in to the venturi adjacent to the main nozzle. The progression momentarily allows additional fuel to help the transition from idle to the main circuit, a mini accelerator pump. Acceleration can start and the transition to the main circuit begins.
Tuning the idle circuit is very important so that the tuner can get proper acceleration and throttle response. Without the idle circuit the engine cannot idle or accelerate.
Even though the kart line of Dell’Orto carburetors are referred to as needle carburetors the function of vacuum is important to understand.
In the next tech piece on Ekartingnews, we will discuss the importance of the air and fuel ratio.
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