If you had a carb which has a stock jet size of 80 and you live or race at 2000 feet above sea level, then you would use a 79 Holley jet in the carb. You can do this without a meter, but it is a bit tougher. Start with the factory jetting and proper float levels. 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. If you are experiencing a bog or hesitation off idle, you can try a larger, higher shooter size. You always want to go a bit rich, as excessively lean mixtures will cause damage to your engine, create pollution, and give you bad gas mileage and performance. On some Holley's, there is a steel check ball in the passage that actuates the diaphragm.
There is a cork gasket on the choke housing that matches up to this port. Later when Holley came out with aftermarket versions of the carb - both in 4150-series versions and the cheaper 4160-series ie - with a secondary metering 'plate' they were still rated at 780 cfm in the earlier catalogs and then, in later catalogs at 750 cfm. That is the air inlet to the choke coil housing. You may need to adjust the external spring one way or the other to get it tight at idle, yet still have the. You then put a vacuum gauge on the engine to tell you what circuit is working at the particular time that you are lean or rich. Manifold vacuum is what pulls fuel from the lower parts of the carb, where the idle feed and transition slots are.
Main Metering: The booster venturi that thing sticking out into the throat of the carb supplies the major portion of the fuel at cruise and power levels. Trying to align the screw holes while keeping the spring compressed is a quick way to pinch off and tear the diaphragm. Keep in mind that the stock jetting listed is for applications at sea level and at 70 degrees carb inlet air temperature and is meant to give you the baseline calibration. If you, or a spotter, can see puffs of black smoke when the secondaries open, then it is too rich. I suggest you purchase a Holley rebuild kit and rebuild the entire carb, because the cost of two float valves is almost as much as the costs of the entire rebuild kit. Similarly, a change in the carb's inlet air temperature may require a change in the jet size from the stock calibration. If you want a mechanical secondary carb, you must start out with a mechanical secondary carb.
You have the instrumentation to figure out what you did wrong if it does not work the way you expected it to, so there is no harm done. The idle circuit allows a very small amount of finely metered fuel into the engine. These sensors are used in electronically fuel-injected cars as a signal telling the computer whether to supply more or less fuel. There is an idle circuit in the rear barrels of your Holley, too. Inconsiste nt idle speed Many people lately have been asking me about idle problems where they will set the idle at 800 or so, then when they drive the car or boat, the idle only comes back to 1500 or so.
Among many other things, the catalog lists every performance and race carburetor they make and the indivdual specifications for each carb. On a manual transmission vehicle, hook up the vacuum gauge and take the reading with the engine at idle. Vacuum secondary carburetors have vacuum passages built into the body of the carb to provide vacuum to the secondary diaphragm, which operates the secondaries when there is enough airflow going through the primaries. When they blip the throttle, it will come back to 800. Graphical interpretation of these systems: These bar graphs not to scale illustrate the fuel flowing through your Holley at different stages. There should be zero clearance or a slight preload on the linkage arm to the accelerator pump lever. It consists of either a small ball held down by a steel cylinder, or a sharpened steel cylinder.
Therefore, if you find that your car will not run properly with a jet that is within 5 sizes one way or the other of the factory recommendation, you have problems somewhere else, like a bad or misadjusted float, bad needle and seat, a vacuum leak, a dirty carburetor, or a plain old worn-out carburetor. You can change the springs and change the opening moment. Alternatively, tie a bread bag twist-tie onto the vacuum secondary shaft near the top where the shaft would move in to the housing, and see if it has moved after driving the car. . The vacuum signal stays high for good throttle response at low and mid range rpms.
This is not recommended, except for experts. First you will need to check the adjustment on the pump. If idle speed increases, lower it by closing the idle speed adjustment. This number is used to identify the carburetor and also used when needing service parts or renew kits. Holley has really updated their website, and has now included installation instructions for you to download, print, and read. Vacuum secondaries operate off engine rpm and load, not just rpm, and there just is not enough airflow in a no-load situation to open the vacuum secondaries. Be assured with Holley Renew Kits.
The threads on this sensor are the same as a small-block Chevy gasket-style spark plug, so the bung can be made from one of those spark plug anti-foul adapters. Why don't we just put leaner jets in them to get mileage? Position the rubber diaphragm on the base in the correct orientation. Smog carbs work well on stock engines only, and you cannot expect them to work well on a modified engine, especially one with a loped cam. What do you do with it? Vacuum Secondaries Vacuum secondaries allow a person to run a carb that most people believe might be too big for a particular engine. Of course, you can also just convert the carb to a 4150 style with the metering block and retain the stock single inlet configuration. Answer: Not at all The Holley spreadbore carb is a poor imitation of the Rochester Quadra jet.
There are some exceptions of course. If the fuel does not just trickle out of the sight hole when you rock the car back and forth lightly, adjust the float up until it does. If you know enough to be dangerous when tuning your carb, but not enough to get it right, you need to read this! The high readings are rich, the low readings are lean. The factory determines jet sizes using several factors on each carburetor, including the air bleed size, the venturi size, booster venturi size and shape, and the power valve channel restrictions. Yet the carburetor is most often blamed. Secondary Jetting This is a much more difficult task to tame, due to the acceleration most vehicles provide when the secondaries are open.
Plug fouling may become a problem at part throttle. Holley sells individual cams or you can buy their kit which includes an assortment of cams to choose from. Blown Power Valve You may notice a bad power valve because you will not see the jump from lean to rich when your vacuum gauge gets to the power valve setting. However, some problems can result with radically-cammed machines equipped with automatic transmissions. In fact, stock, production, low performance motors will fall around 75%-85% volumetric efficiency. See the section on power valves below.