SmartCarb metering rods are precision machined with an angled flat on the down-stream side of the metering rod. The flat, called a grind angle or fuel profile, varies between different metering rods in order to suit the fueling needs of a wide variety of applications, engine characteristics, modifications, and fuel selections. Note that elevation and temperature changes are not considered in metering rod selection due to the SmartCarb’s automatic air density compensation features.
Optimum SmartCarb performance requires both the correct metering rod fuel profile for the given application’s fueling needs and the correct positioning of that profile using the Clicker adjuster on top of the SmartCarb. The bottom end or idle and off idle response is tuned first with assessment of the mid to top performance occurring after. Should the application require either more or less fuel through the mid to top range, a different metering rod selection may be advised.
The fueling differences between rods in the same series are minimal if not identical at idle at the same Clicker setting. Two different rods in a given series will progressively diverge from one another in how much or little fuel they provide through the throttle range relative to one another with the biggest differences occurring at full throttle or wide open. Metering rod richness or leanness is given by the number, with lower numbers being richer and higher numbers being leaner.
View the SmartCarb Metering Rod Guide for more detailed information.
Please refer to your SmartCarb User Manual for instructions on changing metering rod. Digital manuals are available to view/download here.