Tuning these emulsion jets should be left to the experts, but the basic premise is that these emulsion jets introduce air into the main metering circuit. Unless you already know all about Holley metering idiosyncrasies, these emulsion circuits should be left to professional tuners. The moment the throttle linkage moves, fuel should exit the nozzle. Place your foot on the brake, engage a gear and record the reading. If you want a mechanical secondary carb, you must start out with a mechanical secondary carb.
What is a Core Charge? This is where a dynamometer would come in handy, allowing testing to be done quickly and concisely. Put it all back together, check for leaks, then drive it until the engine is warm. Don't tap into just one runner, though, as sometimes this will give funny readings. Therefore, it is impossible, due to the passages built into the body of the mechanical secondary carburetors, to switch a mechanical secondary carb to vacuum secondaries. While this passage is called an air chamber, fuel still resides in this chamber at the same level as the fuel in the float bowl. Always install the filter as close to the carburetor as possible, as this is the best location to avoid heat. There are some exceptions of course.
Below are part numbers and links to a common retailer, to which I am not affilliated. But digest each of these and they will generate the energy to get your started on the path to pure Holley comprehension. During oil pressurization, slowly rotate the crank two full turns. Because of the massive amount of compressed air that the blower moves for a high-horsepower combination, the carburetor has to meter a bunch of fuel. Secondary bowls have jets situated ahead of the bowl and fuel , which creates the momentary fuel loss problem. Your carburetor requires 4 to 7 psi of fuel supply at all times, under all conditions.
Place the base on top of the vise and slide the diaphragm through the lower half until it sits flush. Change the jets whenever you increase the performance characteristics of the engine. Be careful here to not catch the rubber with the threads of the screws. Depending on the volume of fuel required for the particular engine, a —6 size is usually adequate for street engines; a heavier-breathing performance engine may be better suited to —8 plumbing. A dragster with a 454 will require vastly different carburetion than a motorhome with a 454! Slip the tube nut over the tube first, followed by the ferrule.
The opening rate of the vacuum secondary system can be tailored by changing the spring inside the vacuum housing. The engine will be sluggish at low rpms, and just won't run right. Having spark plugs foul out with dry sooty deposits is a direct result of excessive fuel. How to know if your vacuum secondaries are opening You can tell if your secondaries are opening by keeping them shut with a spring or other means. I Full manifold vacuum source: Outlets for constant manifold vacuum.
You can identify these carbs by the four vertical holes adjacent to the air cleaner stud that allows air controlled by the adjustment screw to bypass air past the throttle blades. G Curb idle transfer passage: Machine passage for idle fuel discharge to secondary side with two-port idle mixture screws for more even idle fuel entry into engine. Be sure to choose an electric pump that is designed for use with the lower pressure required for a carburetor. The trick here is to size the power valve roughly 1. If the carburetor has mechanical secondaries, verify that the secondary throttle plates are opening.
This means the power valve will open at 8. Likewise a carburetor with vacuum secondaries will only open the secondaries enough to feed the engine what it needs. In place of the jet block is a special metering plate. The color coded springs run from light tension to heavy: White - Lightest Yellow Short Spring Yellow Purple Plain Steel grey Brown Black - Heaviest If there is a bog or hesitation when the secondaries open, the spring tension is too light, go to the next heavier spring. The engine should be warmed to normal operating temperature to make sure that the fast-idle cam was released before final adjustments. I own at least 9 different books on Holley carbs, several general repair manuals that cover the Holley, and have cut out many articles from Car Craft, Hot Rod, and other magazines.
If the engine shows performance problems such as stalling or sluggish acceleration, you'll need to change the jet sizing. Back to All photographs and content on this website are copyrighted by the author. When custom bending is required, aluminum fuel tubing is easier to work with and is also more manageable for flaring. Take a look at the plugs. In a properly adjusted curb idle setting, the tip of the throttle blade should just uncover the end of the transfer slot as shown here.