Basic Holley Carb Rebuild – Part 2

This is part 2 of the Basic Holley Carb Rebuild. If you haven’t read part one yet, it can be found here. In this article I will cover the reassembly and initial set up of your Holley carb.

Picture of carb gaskets

 

Now that your carb parts are clean and dry and you acquired the replacement items that you need, we can begin reassembly. Start by checking all of the new gaskets and parts against the old pieces that you saved. Make sure that all the passageways on the gaskets are the same. See the photo. The new gaskets are on the bottom row.

 

Place the carb upside down on your carb stand, set the gasket in place, and attach the baseplate to the main body.

Picture of Carb base plate assembly

 

Snug the screws equally before you begin to tighten them fully. As per Holley Technical Support, finish tightening them in a criss-cross pattern to 30 in./lbs. If your carb is so equipped now is the time to mount the vacuum secondary and the choke assembly to the main body. After you’re finished turn the carb over and place it on your carb stand.

 
Picture of Power Valve Block off Plate

 

Prepare to mount the secondary metering plate and fuel bowl to the main body. Take a look at the photo for the order of assembly.

 

 
Picture of the Metering Plate attached to the Main Body

Place the bowl gasket on the main body first, then the secondary power valve block off plate, after that the secondary metering plate gasket, and finish up with the metering plate. Find your clutch head screw driver and tighten the screws in a criss-cross pattern.

 

 

 

Before mounting the secondary fuel bowl to the main body check the float height and adjust it if necessary.
Picture of Setting Float Level

As per Holley Technical Support the secondary float height is 13/64 for this carb. That’s .203. I am using a # 7 drill bit at .201 to set the clearance between the float and the top of the fuel bowl. Bend the tab that rests on the fuel inlet needle to adjust the float up or down to achieve the desired clearance.

 

 

 

Place your new fuel bowl screw washers on the four secondary bowl screws. Mount the secondary fuel bowl to the main body and snug up the bowl screws. As per Holley Technical Support, finish tightening them in a criss-cross pattern to 30 in./lbs.

Picture of Transfer Tube

 

Put the O-rings on the ends of the fuel transfer tube with a little oil for lubrication, and then push the tube back into the secondary fuel bowl as shown in the picture.

 

 

 
Picture of Accel Pump Transfer TubePut the O-rings into the groves on the ends of the accelerator pump transfer tube with a little oil for lubrication. Push the tube into the main body as shown in the picture.
NOTE: The original O-rings in this carb were brittle and cracked and needed to be replaced. Check yours if your carb is so equipped.

 

 

 
Picture of Carb Main Jets

Start assembling the primary metering block by placing the gasket on the power valve and screw the power valve into the metering block. Tighten with a 1 inch socket or wrench.
Carefully screw the main jets into the metering block with either a Holley carb jet tool or a large blade screw driver.

 

 

 

Before mounting the primary metering block and fuel bowl to the main body check the float height and adjust it if necessary.
Picture of Setting Float Level

As per Holley Technical Support the primary float height is 3/16 for this carb. That’s .187. I am using a # 14 drill bit at .182 to set the clearance between the float and the top of the fuel bowl. Bend the tab that rests on the fuel inlet needle to adjust the float up or down to achieve the desired clearance.

 

 

 

Place the metering block gasket on the metering block, and fit the block to the main body. Pay attention to the accelerator pump transfer tube. You will have to push the metering block toward the main body to seat the tube into the block.

Place the primary fuel bowl gasket onto the front of the metering block. The guide pins will align and hold the gasket in place. Check to make sure the gasket is correct for the accelerator pump fuel passage for your carb.

Place the primary fuel bowl on the metering block by carefully inserting the fuel transfer tube into the bowl, and simultaneously placing the accelerator pump levers into position.

Place your new fuel bowl screw washers on the four primary bowl screws and snug up the screws. As per Holley Technical Support, finish tightening them in a criss-cross pattern to 30 in./lbs.

Picture of Fuel Transfer Slot

Turn the carb over and place it on your stand. Check the relationship between the primary throttle blades and the idle speed fuel transfer slots. A small portion of the slot should be exposed by the throttle blades at idle. This is adjusted by the idle speed screw. See the arrows in the photo. During this particular rebuild I did not touch the idle speed screw at disassembly, and there is no adjustment necessary now as the amount of the transfer slot that is exposed looks perfect.

 

 

 

Picture of Reverse Idle Mixture ScrewThis model Holley carb is equipped with what is called a backwards idle mixture circuit. That means turning the screw clockwise richens the mixture. There is also a plastic cap on the screw that limits the range of adjustment. Set both mixture screws in the center of their travel. See the photo. On Holley carbs without this backwards idle mixture circuit, the mixture screws are turned in until just seated and then turned out one and a half turns as an initial setting.

 

 

Check the accelerator pump linkage adjustment. There should be absolutely no slack between the pump diaphragm lever and the actuating lever screw. The slightest movement of the throttle should depress the diaphragm lever. Turn the screw counter clockwise while holding the nut to take up any slack.

Picture of Accelerator Pump Adjustment

NOTE: There should be at least .015 of travel left in the diaphragm lever at wide open throttle. Check this with a feeler gage. See photo.

NOTE: Anytime the idle speed screw is adjusted you must go back and check the accelerator pump linkage adjustment. Make sure there is no slack and that you have at least .015 of travel left on the diaphragm lever at wide open throttle.

 

 

The carb is now ready to bolt to the intake manifold. Use a new carb base gasket and as per Holley Technical Support, tighten the stud nuts in a criss-cross pattern to 60-80 in./lbs. Connect all linkages and make sure there is nothing binding. Connect your fuel line and check for leaks as soon as you begin to start the engine. Start the engine and fine tune the carb per standard procedures.

If you would like to learn more about tuning and modifying Holley carbs I highly recommend two books.  I am making these recommendations based on my personal experience with tuning and modifying carburetors using them as a guide.

Disclosure: The links below are affiliate links and I will receive a commission if you make a purchase.

Picture of Holley Carburetors by Mike Urich & Bill Fisher

 

Holley Carburetors by Mike Urich & Bill Fisher is a great all around reference for Holley carbs. You are looking at my well-worn copy from 1972. It has been updated over the years to include Holley Fuel Injection. If you are interested please click here to check it out.

 

 

 

Picture of Holley Carburetors by Dave Emanuel

 

Super Tuning and Modifying Holley Carburetors by Dave Emanuel is a great reference for modifying Holley carbs. If you are interested please click here to check it out.

 

 

I hope you have found the Basic Holley Carb Rebuild article helpful. It is intended to show those on the fence about rebuilding their carburetor that with a little care and patience it is easy.

 

I value your comments, suggestions, and opinions. Please leave a comment below.

It’s all about the car!

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    2 Responses to Basic Holley Carb Rebuild – Part 2

    1. michael smith January 16, 2016 at 6:16 pm #

      I recently purchased a used holley that needed rebuilding. the gaskets were in reched condition. I tried to rebuild and am unsure if I used the right metering gaskets. mine only has one metering block and I am not exactly sure how to know exactly which 750 I have here. is there any way you can help me? I did good on everything else, I think. im not sure about this (vent baffle) it didn’t stay in place and got caught under my float bowl. I have carb on bench now while I scratch my head and wish i’d paid an old man to assemble.

      • Richard Horton January 18, 2016 at 7:21 pm #

        Hi Mike. Find out exactly what carb you have so you can make sure you have the right gasket. Take a look at the first carb article here. The second picture shows you where to look on the choke horn for the carb list number. There is also a link right there to Holly’s carb numerical listing PDF. There you can look up your carb and find the right gasket numbers. You can purchase them anywhere on line once you have the right number. The vent baffle goes under the fuel bowl gasket. Check that you have the right bowl gasket while you’re there. Take your time. I’m sure you’ll get it right. If you have any more questions please let me know.

        Richard

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