What is a Carburetor?

CFS Carbs

As we all know, a carburetor is a devise that regulates the air flow and fuel flow into an engine. But what is it, really? Well, a carburetor is essentially a mechanical computer. To do its job on an engine, and do it well, a carb needs extensive "preprogramming". By preprogramming, I mean the design and fuel calibration of the carb. There are many aspects of a carb's design that can make or break its ability to be successful on any particular engine. The carb's venturi and throttle bore sizes must be chosen to be compatible with the engine's cubic inch displacement, and more importantly, to its horsepower capability. So, obviously, the one size fits all approach does not work well, particularly when there is a really wide range of engine sizes and horsepower levels, like we have in tractor pulling.

The relative sizes of the venturi and throttle bore need to be chosen so that the carb has good part throttle drivability, as well as adequate wide open throttle flow. In other words the carb must work well over a wide range of part throttle and full throttle conditions. This is particularly true in tractor pulling , due to the nature of the competition, particularly in pace pulling. The carb must have to ability to regulate the engine's power and the tractor's speed, simply from the amount of throttle that the driver is using at any one instant in time during the pull. In other words, it must act like a very smooth rheostat works. A huge key to attaining this capability, is the fuel calibration of the carb, and how that works with the carb's venturi and throttle bore dimensions, as well as the characteristics of the engine itself. A smaller carb that meters fuel efficiently, will typically outperform a bigger carb that meters fuel poorly. The key to allowing an engine to perform to its full potential, is using a carb that doesn't restrict full throttle power, and also gives the engine very controlled drivability at part throttle.

The fuel calibration of a carb, any carb, needs to be adjustable, to be able to accomplish the fine tuning that is necessary to get the engine to perform to its full potential. That is why having changeable jets and air bleeds is as essential to the tuning process, as are fuel pressure and idle mixture and idle speed. This applies to both the low speed(part throttle) circuit as well as the high speed(main metering) circuit. Once a well designed carb has been fine tuned to the characteristics of the engine it is on, then the best competitive capability of the engine has been attained. Then it is up to the tractor driver to use that power to get the best possible pull, as the track conditions and class rules will allow.

Norm Schenck / Competition Fuel Systems / Birch Run, MI. / [email protected] / 520-241-2787 / www.compfuelsystems.com/index.html

This post was edited by CFS Carbs on 12/06/2023 at 11:42 am.

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