Smartcarb A-Q09 Metering rod

Lower numbers are richer (more fuel) and higher numbers are leaner (less fuel).

The SmartCarb is a single circuit fuel system that uses a metering rod to provide fuel flow through the entire throttle range. 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 performance from the SmartCarb requires both the correct metering rod fuel profile for the given application’s fueling needs and 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. The Clicker raises or lowers the metering rod independent of the throttle slide. Clicking to the right or clockwise raises the metering rod which moves the fuel profile in the richer direction. Clicking to the left or counterclockwise lowers the metering rod, moving the fuel profile in the leaner direction. In short, click Right for Rich (RR) and Left for Lean (LL).

Note that the fueling differences between rods in a series are minimal if not identical at idle. Two different rods 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 being at full throttle or wide open.

Most applications for which solid tuning baselines have been established will use one of two or three metering rods, depending on a few factors. For example a stock 2019 KTM 300 XC will use the A-Q11 in most cases, however the A-Q09 may be better, providing more fuel through the mid to top to accommodate a high compression head, hotter ignition, race fuel, and/or if the bike is seeing harder than normal engine loading (supermoto, desert racing, hill climbing, or snowbiking).