Considerable mystery surrounds the tuning of the secondaries on a holley carb. 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.
Tuning Tips
Holley carb jetting 101. The as delivered jetting from holley is very close to optimum for the majority of high performance applications. Now holley efi products power these cars and are dominating the performance world. For example at wide open throttle the engine runs poorly according to a jetting chart the jet to adjust is the main jet. 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. Vacuum secondary tuning. For every 2000 foot increase in altitude you can reduce the jet size by one size.
Holley has been the undisputed leader in fuel systems for over 100 years. In fact it is not at all complex but it can be time consuming. 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. Air valve style carbs with. Mechanical secondary carbs are used in race cars that operate at max throttle. Holley carburetors powered every monster energy nascar cup team and nearly every nhra prostock champion for four decades.
Many will look at jetting charts and infer from it the jet which is affecting carburetor circuit. Since the pilotslow jet is supplying fuel at wide open throttle we always recomend starting with the slowpilot jet. This is more complicated than a simple spring change. Air valve carbs provide the best throttle response on street cars. Tuning the accelerator pump is required to prevent a bog. Power valve tuning theres more to tuning the holley power valve on the primary side than just choosing when the valve opens.
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. Lets say you. They can also be used to give the driver more control. Lets say you have a 750 double pumper holley 0 4779. For the most part the jets delivered with the carburetor should suffice as your tune up baseline.
As mentioned earlier by selecting the correct spring for the vacuum chamber you take care of 90 percent of the tuning of the secondaries. Holley 4 barrel carburater information list numbers and stock jetting. 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.
Gallery of Holley Carb Jetting 101
