Holley 4 barrel carburater information list numbers and stock jetting. Lets say you have a 750 double pumper holley 0 4779.
Carb Class 5 Basic Carb Tuning Tips Holley Blog
Holley carb jetting 101. In a holley carb the jets are located in the metering block behind the fuel bowl. Holley carbs are calibrated for sea level operation and an inlet air temperature of 70 degrees fahrenheit. As mentioned earlier by selecting the correct spring for the vacuum chamber you take care of 90 percent of the tuning of the secondaries. Air valve carbs provide the best throttle response on street cars. For example at wide open throttle the engine runs poorly according to a jetting chart the jet to adjust is the main jet. Holley carburetors powered every monster energy nascar cup team and nearly every nhra prostock champion for four decades.
For every 2000 foot increase in altitude you can reduce the jet size by one size. Air valve style carbs with. Tuning the accelerator pump is required to prevent a bog. Now holley efi products power these cars and are dominating the performance world. In fact it is not at all complex but it can be time consuming. Power valve tuning theres more to tuning the holley power valve on the primary side than just choosing when the valve opens.
Tuning a performance street car for its best performance even if you have outside air ducted to the carburetor is a constant job or at least seasonal. One of the things we noticed over the years is the lack of information concerning holley list numbers and the specifications for individual carburetors and their stock jetting. The ducting will help even out the seasons a little but the engine transferred heat is still hanging around causing troubles and requiring a little bit of attention from you. Mechanical secondary carbs are used in race cars that operate at max throttle. Once you know the correct stock jetting for your particular holley carb you can determine whether you live or race at an altitude above sea level. This is more complicated than a simple spring change.
Vacuum secondary tuning. Lets say you. The as delivered jetting from holley is very close to optimum for the majority of high performance applications. Many will look at jetting charts and infer from it the jet which is affecting carburetor circuit. Considerable mystery surrounds the tuning of the secondaries on a holley carb. Since the pilotslow jet is supplying fuel at wide open throttle we always recomend starting with the slowpilot jet.
They can also be used to give the driver more control. Holley has been the undisputed leader in fuel systems for over 100 years. For the most part the jets delivered with the carburetor should suffice as your tune up baseline.
Gallery of Holley Carb Jetting 101
