Valve seat or race engine with a long duration

Posted by zjautopartsLee on February 3rd, 2016

Refer to the Carburetor float sheet chart, and look for a number closest to that found in Step 8. (In this case, 6.319 refers to a 71 main jet.) Repeating Steps 1 through 8 for each of the carburetor venturii is required in order to find the jet that each should run.

On the secondary side of the brother-in-lawed carburetor, the jet size ended up being a 74 main jet (82.83 x 8.2 percent = 6.792), and the nearest number on the fuel sheet chart is 6.709.

Each Holley power valve is stamped with a number to indicate the vacuum opening point. For example, the number "65" indicates that the power valve will open when the engine vacuum drops to 6.5 inches or below. To determine which power valve to use, an accurate vacuum gauge should be used.

Valve seat or race engine with a long duration, high-overlap camshaft will have low manifold vacuum at idle speeds. If the vehicle has a manual transmission, take a vacuum reading with the engine thoroughly warmed up and at idle. If the vehicle is equipped with an automatic transmission, take the vacuum reading with the engine thoroughly warmed up and idling in gear.