Instructions to Rebuild a Holley 4150by Kelvin Hayes
The Holley 4150 is one of the most widely used carburetors in Holley's extensive lineup of fuel delivery systems. Holley has even dedicated a video series to tuning, adjusting and rebuilding the 4150. The 4150 is a 4-barrel, single-pumper carb with an air flow rating of 750 CFM (cubic feet of air flow per minute). Holley and a number of third-party manufacturers market rebuild kits for the 4150 that will refresh the carburetor's inner components and return it to its original performance levels.
Unscrew the four corner bolts from both the primary and secondary fuel bowls, using a 5/16-inch socket wrench. Pull the bowls from their metering blocks. If the bowls stick, do not pry them off. Instead, tap them with the handle of a screwdriver until their seal is broken. Discard the gaskets from both bowl assemblies. Place all the parts of the carburetor in a cleaning tray.
Unscrew the mounting screws from both metering blocks with a screwdriver, pulling the metering blocks off the main body. Discard the gaskets. Remove the power valve from the primary metering block with a 1-inch closed wrench. Some versions of the 4150 will have a power valve in the secondary metering block. If this is the case, remove it with the 1-inch closed wrench, screwing it out of the back side of the metering block(s). Remove the main jets (two each) in the primary and secondary metering block, using a screwdriver.
Note the size number stamp on the power valve(s). Ensure that you replace the power valve with the same size during the rebuild.
Turn the carburetor upside down and unscrew the base plate screws (4), using a screwdriver. Pull the base plate and gasket off the base of the main body. Match the gasket pattern of the original gasket to the correct gasket from the rebuild kit and discard the old gasket. Return the carb to an upright position and unscrew the fuel nozzle screws from within the throttle bores with a screwdriver. Pull the nozzles out with pliers. Ensure that the nozzle needles remain within the nozzle seat holes in the throttle bore. There's no need to remove these.
Spray the entire exterior and interior of the carburetor with compressed air and carb cleaner spray. Spray every hole, orifice and channel to ensure all debris and fuel residue is removed. Inspect each surface that had a gasket pressed against it to ensure no gasket remnants remain. If you find gasket remnants, scrub them off with a soft toothbrush. Rinse the carburetor's interior sections with carb cleaner spray again.
Rebuilding The 4150
Place the fuel nozzles on their seats within the throttle bore and insert the nozzle screws in the tops of the nozzles. Tighten the screws with a screwdriver. Flip the carburetor over and place the base plate gasket on the base of the main body, ensuring all holes line up. Place the base plate on top of that and screw in the base plate screws, using thread lock tight on each screw. Turn the carb upright.
Insert the power valve O-ring in the power valve cavity, then screw the power valve into place on the back side of the metering block with a 1-inch box wrench. Press the metering blocks to the main body, along with new gaskets. Screw the metering block screws to the main body and tighten. Screw each set of main jets in the metering blocks (one set per metering block) with a screwdriver. Slide the final metering block gasket over the front face of each metering block and press the fuel bowls over their respective metering blocks. Tighten the corner bolts on each fuel bowl to 8 foot-pounds of torque with a torque wrench.
Unscrew the faceplate screws from both the accelerator and vacuum pumps. The accelerator pump is found on the front (primary) fuel bowl, while the vacuum body is on the passenger side of the carb, near the choke body. Remove these screws with a screwdriver and pull the face plates off. Pull the pump diaphragm from both pumps and insert their replacements. Install the face plates and tighten the screws to secure the face plates.