Demon Carburetion has released a new calibration kit that enables engine tuners to dial-in exact air-fuel ratios for each specific engine.
Whether additional fine-tuning is precipitated by altitude, exotic cam, high-compression, or engine displacement, or uneven distribution from an intake manifold at different engine speeds, this new calibration kit will fine-tune the fuel curve.
It provides four different sizes of primary jets, six different sizes of metering rods, four different weights of metering rod springs, and two different sizes of secondary jets. All components are supplied in pairs and all jets and needles are stamped for easy identification.
Generally, the metering rods are changed to adjust air-fuel ratios in finer increments; the jets are changed to adjust air-fuel ratios in larger increments. The tuning kit eradicates eye-watering exhaust fumes or puffs of smoke under acceleration. At the chassis dynamometer it enables the tuner to accomplish maximum efficiency.
Street Demon metering rods reside in the primary jets only. At their lower ends the metering rods have two steps: an upper and a lower. The upper step has a larger diameter that functions at idle. At idle the metering rods, each of which is attached to a small piston, are drawn downward by vacuum into the primary jets and the idle fuel is metered accordingly. At off-idle and cruise conditions, as vacuum diminishes, they pop up to the next step—the smaller diameter step—which increases fuel flow. The primary tuning parts are used to tune idle, off-idle, cruise and mid-range while the secondary jets are often altered for full-throttle conditions.
The spring options are used to ensure the metering rods are fully lowered at idle. This activity can be witnessed by opening the two small covers above the metering rod chambers on top of the carburetor. If the primary needles are bouncing or not being pulled down fully to the idle position, a weaker spring is required.