Each Holley carburetor comes with factory jets set for sea level elevation and a temperature of 70 degrees. For every 2,000 feet in altitude change, or 35 degrees of temperature change, the jets will need to be changed to maintain proper fuel delivery. For example, during cold conditions, an increased jet size will allow more fuel into the combustion chamber, compensating for the lower engine operating temperature. According to Holley, the best indication of proper jetting is found by examining the spark plugs after they've cooled.
Unscrew the four bolts that attach the fuel bowl to the carburetor metering block. As you pull the fuel bowl off, save the two gaskets that seal the fuel bowl to the metering block, you'll reinstall those after swapping the jets.
Unscrew the jets counterclockwise from their seats in the metering block using a flat head screwdriver. The jets are easily recognizable as the brass bolts with holes drilled through their center.
Screw in the set of new jets, based on the recommended size for your altitude and temperature. Larger plenum intake manifolds may require a larger jet size, even if you remain near sea level and around 70 degrees. This is due to the increased air flow the larger intake provides.
Place the gaskets on both the metering block and fuel bowl, and press the fuel bowl to the metering block. Ensure that the gaskets are properly installed and are not folded or distorted.
Insert the four fuel bowl screws and tighten them with a socket wrench.
