A friend is restoring a 1976 Corvette and he asked me to give the carburetor a once over before it went back on the engine. This carb has been laying around for a number of years collecting dirt so a basic cleaning, inspection, and gasket replacement is necessary.
This article covers a general cleaning and gasket replacement on a Holley Spread Bore carb out of a 1976 Corvette, list # 9895. The process followed here can be used for any 4150/60/75 Holley carb. Disassembly, cleaning, inspection, gasket replacement, and reassembly are covered. This article is not intended as a guide for modifications or performance tuning. If you are looking to learn more about modifications and tuning, I make a few book recommendations at the end of part 2 of this article. Also, you can always post a question in the comments section or use our contact page for help.
Start by locating your carb’s list #. It is located on the choke horn as shown in the picture.
This number is the key to getting the correct parts for your carb. Holley Performance Products has a part number guide in PDF format on their website that lists all of the replaceable parts available for your carb. Here is the link. https://www.holley.com/document/techlibrary_carb_numerical_listing.pdf
Keep all the old parts and gaskets you remove so that you can make sure the replacements match up.
Make sure the carb doesn’t have any fuel in it by turning it upside down over a suitable drain pan. Any fuel will drain out of the bowl vent tubes.
Place the carb upright on a suitable carb stand. If you don’t have one use a cardboard box or anything else that fits the bill. This keeps the carb from resting on the linkage. Note what I am using in the picture. This is the best “free” carb stand that I have found, a plastic Maxwell House coffee container. “Good to the last drop” …. Of gasoline!
Take the primary fuel bowl off first by removing the four bowl screws and note if they are different lengths and keep track of any bowl screw washers present. Some washers come off with the screws and some stay stuck to the bowl. I recommend you replace these as they are cheap insurance against a fuel leak. If you are going to replace them you can remove them now. Tap the fuel bowl away from the main body with a small piece of wood. DO NOT pry it off with a screw driver or you run the risk of ruining the surfaces.
Remove the primary metering block from the main body by tapping a small piece of wood against the metering block in a direction away from the main body. DO NOT pry it off by placing a screw driver between the metering block and main body or you run the risk of ruining the surfaces.
Use a 1 inch socket or wrench to remove the power valve and gasket and set it aside.
Carefully remove the main jets with a wide blade screwdriver. Do not damage the surfaces as this could affect flow. There are many manufactures that sell a tool for this which protects the jet surfaces from being marred. You can remove these without damage with a wide blade screwdriver if you are careful.
Repeat the steps above to remove the secondary fuel bowl and metering block. NOTE: Some Holley carbs do not have a secondary metering block, they have a secondary metering plate as shown in the photo.
The plate is secured by clutch screws. Find your trusty clutch head screw driver and remove the screws. The metal plate you see after the metering plate is removed is called the secondary power valve block off plate. It will come off when you pull off the gasket behind it.
Turn the carb over and prepare to remove the base plate. The Maxwell House coffee container with the lid off is a perfect fit around the air horn of these Holley carbs.
Remove the vacuum secondary and choke assembly if your carb is so equipped. These will not go in the wash.
If your carb has a vacuum secondary you will have to remove the circle clip that retains the actuation rod to the secondary throttle blade shaft. Be careful not to lose this clip. Once you remove the screws holding the base plate to the main body carefully separate the pieces. Pay attention to anything hanging onto the throttle shafts.
Now we are ready for the parts washer.
If you don’t have a parts washer get an old pot or a clean oil drain pan and a few spray cans of carb cleaner. If you are spraying carb cleaner I strongly recommend safety glasses to keep that stuff out of your eyes.
Start cleaning and pay special attention to all fuel passageways and air bleeds.
Clean the inside of the fuel bowls. Note: This particular carb in these photos did not need new needle and seat assemblies so I did not remove the floats for this rebuild. I recommend you at least check the condition of the needles on your carb and replace them if necessary. If you left the floats attached like I did don’t let them bounce up and down in the wash process as they might get damaged.
Clean the base plate, throttle blades, and linkage. Clean the main body and blow out and dry all parts with your air compressor. If you don’t have a compressor dry as much as you can with anything lint free and set aside to air dry.
Now is the time to inspect everything and order the parts you need according to the list # of your carb. When in doubt about whether you need a new part or not, get it. You don’t want to go back and do this again because something is wrong.
Notice the bends in the linkage. This occurs from being tossed around and set down without a carb stand. This needs to be straightened without stressing the throttle shaft. Use extreme care here and make sure the shaft is not binding in the base plate when you are done.
I hope you enjoyed part one of this article. We will cover reassembly and basic set up here in Basic Holley Carb Rebuild Part – 2
I value your comments, suggestions, and opinions. Please leave a comment below.
It’s all about the car!