The carburetor is subject to heat, debris and mechanical wear resulting in sub-par performance. Depending on the current state of your Holley 750 double-pumper, the rebuild process may be quick. But if any section of the base, main body, metering block or fuel bowl is cracked, it may be an involved process. Either way, the rebuild will result in a carb that runs like new. Holley and third-party manufacturers provide rebuild kits that will replace gaskets, O-rings, pump diaphragms, power valves and jets.
Place the carburetor in a cleaning tray and spray all the exterior and interior parts with carb cleaner. This will remove surface grease and allow you to inspect the main body for cracks or defects. If cracks are found, that section of the carburetor (main body, bowl, metering block etc.) will need to be replaced from a donor carb, or by purchasing the part from Holley.
Unscrew the four corner bolts from both of the fuel bowls using a 5/16-inch socket wrench. Pull the bowls off the metering blocks, tapping the top of a bowl gently if it sticks. Discard the gaskets. The metering blocks are now exposed. If you notice that one of the metering blocks does not contain a power valve in its center, this will indicate that this side of the carburetor houses the secondary fuel delivery system that feeds the back two throttle bores.
Remove the power valve(s) with a 1-inch box wrench. Unscrew the two main jets from both metering blocks with a screwdriver. Note the size of the jets and power valve by the number stamped on their heads.
Place the main body upside down (air horn down) and remove the base plate screws with a screwdriver. Note the pattern of the base plate gasket, match it with its replacement from the rebuild kit and discard it.
Return the carb's main body to an upright position and remove the two fuel nozzle screws from within the throttle bore with a screwdriver. Pull both nozzles out with pliers, ensuring that the nozzle needle remains within the nozzle seat in the throttle bore area. Preserve these nozzles, as you'll replace them during the rebuild.
Spray all components of the carburetor with compressed air and carb cleaner spray to remove all debris and fuel residue from the walls and holes of the carb.
Scrub the face of the metering blocks and base plate to remove any gasket remnants. This is key to achieving a strong gasket seal with the new gasket set.
Insert the fuel nozzles in their seats within the throttle bore, and then insert and tighten their screws with a screwdriver.
Flip the carb and install the base plate gasket, followed by the base plate. Tighten the base plate screws. You may use thread locker on these screws to ensure they remain tight under vibration.
Place the carb upright and insert the power valve O-ring in the PVC (power valve cavity) on the metering block. Insert the power valve with a 1-inch wrench and the main jets with a screwdriver.
Rest the new metering block gasket on the face of the metering block and place the fuel bowl against the metering block. Tighten the fuel bowl bolts with a 5/16-inch socket wrench.
Unscrew the caps from both fuel pumps (one on each fuel bowl) with a screwdriver. Pull the cap off and remove the pump diaphragm. Insert the replacement diaphragms from the rebuild kit and install the pump cap again, tightening the screws. Place the carburetor back onto its mount on the intake manifold.
