How to Jet a Holley Carburetorby Francis Walsh
Holley Dominator carburetors have been used in drag racing and performance vehicles for more than three decades. Car owners can adjust the amount of fuel that is fed into the combustion chambers of naturally aspirated engines by changing the size of the fuel jets. Do you have a stumble at the starting line or a lean condition at the top end? By adjusting the jets of a Holley carburetor you can put more fuel into the engine when you need it or take it out when you do not.
Diagnose the problem with the carburetor. Drag racers will report that their car stumbled at the line if there was too much fuel at the start or leaned out at the top end when not enough fuel was sent into the engine during peak RPM. Bring the car to the shop or get it under the awning if you are racing. Park it on level ground and remove the hood assembly.
Grab two small screwdrivers and a set of Holley Jets. For the 706ci using a 94 jet, have a set that ranges from 90-98. The 1150cfm Dominator from Holley will use two metering jets for each fuel bowl. Take the jets and tools over to the engine and find the four screws that secure each fuel bowl and metering block to the side of the 1150cfm Holley Dominator four-barrel performance carburetor. There are two fuel bowls and metering blocks on each Dominator carburetor.
Loosen each of the four screws on one side of the carburetor to remove the fuel bowl and metering block for that side. After loosening each one, you can continue to remove the screws completely. Two gaskets will separate each piece of the float assembly and one for the side of the carburetor. Keep the gaskets that seal these pieces together. With the parts away from the carburetor, you can separate the fuel bowl from the metering block and view the jets that are installed into the metering block.
Choose the next size of jets. Installing a new size of fuel jet will either increase or decrease the amount of fuel that is pushed into the carburetor and burned at each stage of the power band. Change the size of the fuel jets to fix the original diagnosis of stumble (fuel rich) or lean (white smoke, high exhaust gas temperature).
Insert a small, flat-head screwdriver into the notch on the top of one of the fuel jets in a Holley Dominator carburetor and turn it counterclockwise until it is out. Insert a 0.92-sized fuel jet into the opening and secure it with enough torque to seat it firmly. Repeat for the other size 0.94 fuel jet in this metering block. Loosen, remove and replace the 0.94 jet for a 0.92 jet. You have decreased the amount of fuel sent to the engine and this will eliminate a stumble at the line if fuel supply was the issue.
Reconnect the fuel bowls, metering blocks, and gaskets and secure the assembly back to the side of the carburetor after swapping out fuel jets to adjust the carburetor's performance during competitive drag events. Repeat the process on each float and metering block assembly you have. For a dual carburetor setup using Holley Dominator 1150cfm carburetors, there will be eight jets to be swapped and four metering block assemblies with floats to be jetted.
- check Jet extensions are used in some of Holley's Dominator carburetors. Use jet extensions if your lean condition is resulting from jets that are unable to remain fully fueled because of the level of fuel in the bowls. If you have changed jets in your Holley Dominator and a lean condition persists, you can try jet extensions when you tune the carburetor with a new set of fuel jets.
- close Cover open carburetor ports while working on the fuel bowl and metering block assemblies. Tiny pieces of debris can eliminate the efficiency of a quality carburetor.
Items you will need
- photo_camera Nitrousfitz Racing