carburetor tuning made easy

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This is handy not only for atmospheric changes, but sometimes gasoline quality may vary in more remote locations, and the mixture may have to be richened up to prevent detonation.

A semi-similar system is the Holtzman Vari-Flow. In the Holtzman system, the flow is controlled by the pressure in the float bowl. By introducing a slight vacuum in the float bowl, the mixture is leaned out. This is done by installing a Venturi tube in the inlet throat. This vacuum line is then controlled by a dial that adds bleed air from the atmosphere to control the vacuum in the bowl.

You must recalibrate to richen the main jet, since you are not adding fuel but always reducing fuel when vacuum is increased. There is a calibrated minimum bleed hole that prevents it from going too lean. The Vari-Flow unit can also be mounted on the handlebars or the dash. This way, fuel flow can also be adjusted on the fly according to EGT readings.

In addition to the Vari-Flow unit, Barry Holtzman also introduced the Tempa-Flow unit. This unit automatically adjusts the float bowl vacuum though a bleed circuit controlled by the differential expansion of two materials as the temperature changes. This has been a successful product in the Midwest, where temperature changes are more of a concern than altitude variations. It’s a “leave-it-alone” system that changes your calibration automatically with temperature as the season progresses.

I have heard a lot of positive feed-back from users of the Tempa-Flow system. Barry was very active with fuel system innovation for a long time, and you can buy products designed by him at places like Straightline Performance.

Although fuel injection dominates the new machine market, there are still thousands of older sleds out there that use carbs. Trail riders and racers alike are always looking for easier ways to adjust the fuel mixture, and the aftermarket is still providing innovative carb tuning solutions.
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