A 4160 can be converted to a 4150 by adding a secondary metering block in place of the metering plate and swapping to center–hung-float fuel bowls. A 4150 can be converted to a 4160, although it is not a popular modification.
This side-by-side comparison of fuel-bowl styles makes them easy to identify. At the left is a 4160 (PN 1850) carb equipped with a side-hung float. At the right is a 4150 carb with a center-hung float. The 4150 carb has a metering block at the secondary side; the 4160 has a secondary metering plate. A 4160 is easily converted to the 4150 configuration.
4160 Details
This 4160 (PN 1850) carb has the metering block on the primary side (left) and no metering block at the secondary side (right). The secondary side includes a metering plate with no replaceable jets.
The 4160 carb has a single fuel inlet that accepts a slip-on fuel hose. This banjo-style fitting can easily be changed to a banjo fitting with a –6 AN threaded hose-end connection.
Because the 4160 carb has only a front/primary side fuel inlet, fuel is transferred to the rear bowl via this external fuel transfer tube.
Fuel bowls have either side-hung or center-hung floats. This is easy to identify by looking at the shape of the fuel bowl. If it is rectangular without a “V” protrusion on the casting, the bowl has a side-hung float, such as this example (PN 1850).
With the front bowl removed from this 4160-series carb, you can clearly see the jets near the bottom and the power valve at the lower center of the metering block.
When the primary fuel bowl is removed, you can see that the metering block is held to the body by the gasket. Small alignment dowels serve to center the block in place.
This fuel bowl, removed from a 4160-series carb (PN 1850) reveals a side-hung float, meaning that the float is hinged at one side. A side-hung float may be more susceptible to fuel-level changes during hard turns in contrast to a center-hung float that maintains fuel level better during turns.
With the front fuel bowl removed from this 4160 carb, the primary metering block is exposed; it is sandwiched between the body and bowl, and is gasketed on each side. The fuel bowl’s four screws secure both the metering block and bowl to the carb body.
Removing the secondary fuel bowl from this 4160 carb reveals a metering plate, which is secured to the body with six small flat-top screws.
The 4160-series carbs are easily converted to 4150 status: Remove the metering plate and its gasket and then install a metering block with the appropriate gasket and longer fuel-bowl screws.
The front and rear fuel bowls, front metering block, and rear metering plate on this 4160 carb have been removed. Note the external fuel transfer tube on this carb (PN 1850).
A metering plate provides a “fixed” secondary enrichment. A metering block allows fine-tuning with replaceable jets.
4150 Details
This is an example of a 4150 carb (PN 4779). It has 750 cfm, double-pumper operation with jet-equipped primary and secondary metering blocks and mechanical choke.
Holley Double Pumper carbs are available in various finishes, including this traditional chromate.
All 4150 carburetors have metering blocks at both the primary and the secondary sides.
All Double Pumper carbs include a dedicated accelerator pump for the rear secondary side.
Double Pumper carbs have fuel bowl level-checking ports. This carb (PN 4779) has the traditional brass-thread plugs that are removed to check fuel bowl level while adjusting float level.
Center-hung fuel bowl floats have needle and seat float adjustment. To make an adjustment, loosen the slotted plug (which is the lock), turn the hex to make the adjustment, and then tighten the lock.
This street Ultra HP has red billet anodized metering plates and baseplate.
Notice the “V” shape on this fuel bowl casting, which clearly indicates the use of a center-hung float.
Here, the primary fuel bowl has been removed on a 4150 to reveal the primary metering block.
Center-hung floats pivot at the upper center of the fuel bowl and are less susceptible to fuel-bowl level changes