Jim Smart
July 1, 1998

Step By Step

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First, remove the manual choke assembly. An automatic choke is more complex but just as easy to remove. Once these screws are removed, grab the retainer clip that holds the linkage and it’s free.
The vacuum secondary actuator assembly comes out via a couple of screws and a C-clip, shown.
Performance shortcomings manifest themselves in different ways. A faulty secondary diaphragm will keep the secondaries from opening at wide-open throttle. To check the diaphragm’s integrity, push its linkage until it is completely compressed, covering the vacuum port with your thumb. Then release the linkage. If the linkage returns, the diaphragm is leaking and must be replaced.
Secondary diaphragm inspection and replacement is easy. Remove these four screws and release the diaphragm inside. Watch out for the check ball while you’re at it. Our dry-rotted diaphragm must be replaced.
The secondary bowl fuel line is simple on the Shelby Holley. Disconnect the line as shown at both ends.
Both fuel bowls are removed next as shown. Four machine screws retain each bowl.
Each fuel bowl has a center-pivot float on the Shelby and cathedral-bowl Holleys. Check the float for deterioration. When in doubt, throw it out.
The needle valve and seat screw into the front of the bowl like this.
The primary fuel bowl on all Holley four-barrel carburetors contains the accelerator pump. Four screws retain the pump housing. The accelerator pump injects raw fuel into the primary venturis to help the engine transition from the idle circuit to the power circuit as the throttle opens. A faulty accelerator pump will cause the engine to stumble between idle and open throttle. Common problem areas include the diaphragm and spring. Examine the check ball while you’re in there.
The primary metering block is next. Pull the idle-air-mixture screws.
Also pull the power valve. Check the idle-air-mixture screw tips for damage.
Jones Performance tells us one of the biggest problems with carburetor bodies is warpage and distortion of critical surfaces. Even a rebuilt carburetor won’t perform if it has air leaks. Jones machines all mating surfaces for a perfect fit. Does your carb rebuilder do this? Not likely.
Metering block assembly is easy. Check jet sizes and be certain they’re appropriate to your application.
Ditto for the power valve. Proper power valve and jet sizing is important to performance.
Jones Performance is fitting our Holley with an adjustable vacuum secondary actuator. This is a slick little piece from Holley that controls the secondary opening rate. It allows you to dial in performance. Don’t forget the O-ring between the actuator and the carb body.
Reinstall the float assembly first, then the needle-and-seat assembly.
The accelerator pump diaphragm and spring are next.
Jones Performance opts for a different trick when installing the carburetor baseplate. It deletes the two center machine screws (arrows) to reduce the risk of screw ingestion. Eliminating these two screws will not affect performance.
Reinstall the accelerator pump nozzles. Don’t forget the check valve.
Fuel bowls and line are next. Jones Performance installs new hardware for reliability and good looks.
Accelerator pump adjustment is last. The spring-loaded screw should just touch the lever as shown. This will give you a comfortable pump shot.
Here’s our completed Jones Performance Holley. Not only will this carburetor function very well, it will handsomely dress our 289 Hi-Po, because Jones Performance dips the hard parts for an original appearance and installs new hardware. The result is this good-looking piece.

Holley carburetor-rebuild articles have been published by the thousands ever since the first four-throat atomizers appeared back in the '50s. Suffice it to say the Holley four-barrel carburetor has been thrusting posteriors successfully for four decades with no end in sight. Mustang & Fords is no exception to the rule about Holley carb print media. We're right in there with the rest. However, anytime we find a fresh idea out there for improving the venerable Holley, we like to share it with our readers.

Meet Jones Performance Fuel Systems of Southern California. Our 715-cfm Shelby Holley carburetor needed a freshening up after napping atop a 289 High Performance engine that hadn't run in ages. The dry and dusty beast needed a complete teardown along with important steps for improving performance that few enthusiasts ever pay mind.

Jones Performance took a look at our Holley and concluded it was a salvageable piece. Jones knocked it down, cleaned it up, machined those critical surfaces, and reassembled the unit for our cameras.