Buyer's Guides / Parts

Tools for Tuning Holley Carburetors: You Need More Than You Think

Recently I found myself setting up a Holley Ultra XP carburetor. When I looked at my workbench, I was actually surprised by the sheer number of tools laid out. 

I’m one of those types who always puts tools away once I’m done with them, so there were no “extras” hanging out on the bench top either. I mentioned this story to my OnAllCylinders editor, and we figured it might be a good idea to show you those tools and explain what they’re used for.

I also dragged out a good old-fashioned Holley double pumper as another example, since there are some differences between it and the Ultra XP. Different tools are required.

As a secondary tip, you’ll see the green mat I’m using on my workbench. They’re actually cast-offs from my wife’s quilting hobby; she uses these big mats for cutting fabric and laying out designs. When they’re beyond their best-before date, she gifts them to me. They take a lot of abuse and even have built-in ruler and angle measurements.   

Now, back to the tools.

I’m showing you examples of what I have in my collection, and while Summit Racing might not sell the exact same product, they have similar items. If you’re new to Holley carburetors, check out the photos.

A carburetor work stand such as this is something you really can’t do without when it comes doing bench work.  This is an ancient, discontinued Edelbrock job, but Summit Racing carries several types of carb stands.
I use a Moroso drain cup. It allows you to remove one float bowl screw to drain the fuel right down the handle.
Early Holley fuel bowl screws were slotted, but modern fuel bowls use a conventional 6-point screw. I use a 5/16 inch nut driver to remove them.
You’d never think a hammer would be necessary when working on a carb, but you’ll appreciate a small, light rubber mallet when the time comes to remove a bowl. I use it to tap the bowl off instead of prying it off.
To remove a power valve, a 1 inch wrench works perfectly. Obviously, the box end is what does the job.  You can also use one of the dedicated power valve tools offered by Summit Racing.
In order to access the power valve, you’ll need to pry off the metering block. I use this medium size flat blade screwdriver for the job. This size of screwdriver also works to remove slotted fuel bowl screws and sight plugs.
While it’s possible to remove jets with a large flat blade screwdriver, this Holley jet driver eliminates damage to the jet while removing or reinstalling it.
A large Phillips screwdriver is necessary to remove most shooter screws. Hollow shooter screws will require a medium size flat blade screwdriver.
In contrast, the Ultra XP carbs have shooter screws that require an Allen key. I prefer to use a driver handle on a 5/32 inch Allen socket to remove and reinstall them.
To set the float level on most Holley carbs with externally adjustable needle and seat hardware, you’ll need a 5/8 inch combination wrench along with a large flat blade screwdriver.
On newer carburetors such as the Holley XPs, a 3/4 inch open end wrench is necessary to remove the bowl inlet fittings.
A small Phillips head screwdriver is necessary to remove accelerator pump bodies.
In order to adjust clearance on 30cc accelerator pumps, you’ll need a pair of 3/8 inch combination wrenches along with a 0.015 inch feeler gauge (not shown).
50cc accelerator pump clearance adjustment is slightly different. A 7/16 inch and a 3/8 inch combination wrench are required.
A long, thin flat blade screwdriver is perfect for several tasks including setting idle mixture and idle speed, removing and replacing air bleeds, and adjusting the idle bypass valve. It’s my go-to tool for fine tuning and as you can see, it’s well-loved.
To remove and replace a typical AN hose fuel line, you’ll need a 7/8 inch AN hose wrench. It helps prevent cosmetic damage to the delicate fittings.
If you need to adjust the secondary throttle blade stop on a conventional double pumper (to improve idle), a very small flat blade screwdriver will get the job done.
Finally, carb stud nuts typically require a 1/2 inch combination wrench to remove and reinstall. I prefer a wrench to a socket here, because a ratchet and socket makes it pretty easy to overtighten. A big nut driver also works.

One Comment

  1. I believe most people ignore the secondary throttle stop screw. If its out of adjustment, it’s difficult to get these carbs to run correctly.

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