Jetting (Main Jets); Power Valves; Carburetor Specifications - Holley 0-80508S Installation, Tuning, And Adjustment Manual

JETTING (MAIN JETS)

Due to varied applications that a universal performance carburetor will work with, a few tips on jetting are provided to help you
understand their purpose.
1. Out of the box jetting is extremely close for most applications.
2. Carburetors are calibrated at 70° at sea level. Decrease the jet size primary and secondary, one number for every 2000 ft.
increase in altitude.
3. Holley® jets are broached, flowed, and stamped according to flow rate. NEVER drill jets, as this seriously alters flow
characteristics. Stamped numbers are reference numbers and DO NOT indicate drill size.
4. In most cases it will be unnecessary to increase jet size more than four numbers greater than out of the box jetting. Exceptions
could arise when the carburetor is mounted on a very large volume, plenum-ram manifold.
5. Spark plugs provide the best indication of proper jetting. Consult an ignition manual for proper reading of spark plugs.

POWER VALVES:

The number stamped on a power valve, such as 65, indicates the manifold vacuum below which the power valve is operational. In this
case, all manifold vacuums below 6.5" Hg, the power valve is operating. Generally a 65 power valve is sufficient for most high
performance applications that have a manifold vacuum of 12" Hg or higher. However, some problems can result with radically cammed
machines equipped with automatic transmissions. These vehicles often "idle" at 2000 rpm, approx. 6.0" Hg. At this point the main
nozzles are starting to feed and richen the mixture (supplied by the power valve) and the engine will probably "load up". To correct this
problem, install a 45 or 35 power valve. If the engine has a manifold vacuum of 12" Hg or less, a good way to determine power valve
size is take the manifold vacuum at idle and divide that number by two. The answer is the power valve size. This will provide idling and
proper fuel flow under wide open throttle conditions when manifold vacuums seldom rise above 1" Hg.

CARBURETOR SPECIFICATIONS:

CARBURETOR # PRIMARY
METERING
JET
0-80459SA
0-80508S
0-80508SA
0-80783C
0-3310S
0-3310C
0-3310SA
*21 PLATE is equivalent to 75 JET
:
SECONDARY
METERING
JETS OR
PLATE
70 21 PLATE*
70 21 PLATE*
70 21 PLATE*
67 73 JETS
70 21 PLATE*
70 21 PLATE*
70 21 PLATE*
PUMP PRIMARY
DISCHARGE POWER
NOZZLE VALVE
0.031 65
0.031 65
0.031 65
0.028 65
0.031 65
0.031 65
0.031 65
SECONDARY
DIAPHRAGM
SPRING
Black
Black
Black
Black
Black
Black
Black
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