Holly model 4150 mechanical secondary carburetors
are easily identified by these features dual feed Center hun fobel's
the primary metering block and the secondary metering block
there's one accelerator pump located on each fuel bowl
dual pumps indicate the famous Holley double pumper and can be easily spotted by
noticing 2 accelerator pump arms on the base plate
4150's are designed to fit to a square bore in take bolt pattern
but you can also use an adapter bolt to spread your intake there's a lot more
to 4150 mechanical secondary carburetor
come in for a closer look inside let's start with the throttle body
this component is also referred to as the base plate
and might have a few vacuum port configurations most Holley carburetors
generally have at least one large port that's intended
for drawing in crankcase fumes from a PCV valve and one other smaller port
that's meant for hooking up an accessory that might require full vacuum
if your base plate has two larger reports ones meant for PCV
and the other could be used for connecting to a power brake booster
keep any unused ports plug with a cap to eliminate any vacuum leaks
on the base plate a 4150 mechanical secondary you'll notice an arm that'll
operate the accelerator pump
of the front fuel bowl diagonally opposite you'll see an identical arm position to
do the same to the accelerator pump
of the rear bowl the presence of 2 accelerator pump
arms will signify a double pumper setup the throttle plate assembly
also has a curb idle adjuster screw on the driver side
which sets the idle speed of the engine by opening and closing the primary
throttle plates
and allowing more air to enter the engine on the passenger side
you'll find the fast idle cam adjustment screw for models with electric
chokes
the main body the 4150 will have a choke horn and choke plate
that control the airflow amount during engine warm-up
under the choke plate you'll find the two primary venturi bores and boosters
you'll also find an accelerator pump discharge nozzle that's also sometimes
called a squirter
on a mechanical secondary 4150 model the rear area
of the main body also has a discharge nozzle for the secondary venturi is
the volume and duration a fuel flow through both squirters can be customized
with accessory kits
Holley offers different size discharge nozzles for the body
and you can switch to 1 of many different accelerator pump cam choices
these cams for the front and rear accelerator pumps are changed out on the
throttle plate assembly
to further tune the system back on the body the front and rear venturi
have four small holes
that are the air bleeds for the primary idle and main
fuel metering systems the outer 2 are for the idle circuit
and the inner 2 are for the main circuit these holes should always be
kept free of debris and can be flushed out with carburetor cleaner as
maintenance
like all Holley carburetors the 4150 has a primary metering block that will have
two primary jets to control
normal fuel flow and a power valve that will act as an auxiliary fuel supply
during acceleration
idle mixture is set by adjusting the idle mixture screws located on each side
of the metering block
on a model 4150 just above the passenger side
idle mixture screw you'll find a small vacuum port
this is called the timed or spark advance vacuum import
at idle this port will show little or no vacuum to keep the distributor
from advancing prematurely if you have a mechanical advance distributor
you need to plug up this port all 4150 mechanical secondary carburetors come
with dual feed
Center hung float bowls inside a dual feed bowl
there's a float that's fixed in place with the center mounting hinge
that will press on a needle and seat assembly its positioned above
the float and seat work together to control the fuel level in each fuel bowl
on top of the ball for most models you'll find in adjusting nut
that will control the level of fuel inside the bowl
on this model carburetor on the bottom exterior of both the primary and
secondary fuel bowls
you'll find an accelerator pump the accelerator pump arms are affixed to the
base plate
and press against the diaphragm inside the accelerator pump
on a mechanical secondary model you'll find one on the rear as well
dual accelerator pumps are the defining feature of a Holley 4150 double
pumper carburetor
these pumps are activated every time the throttle is pressed
and will send fuel immediately to the primary and secondary squirters in the
body
4150 model carburetors also have a secondary metering block
with mechanical secondaries in the rear metering block you'll find Jets
installed
and in some cases a secondary power valve as well
back here is where you'll notice the additional accelerator pump at the
bottom of the rear bowl
of this double pumper carburetor now let's go over the passenger side of the
carburetor
with these models of carbs the rear throttle plates are tied directly to the
primary throttle lever
with a connecting link this means that your manually controlling the opening
and closing
of the primary and secondary plates inside the body
as you operate the throttle lever of a mechanical secondary carburetor
the final component to review is the choke assembly
with a manual setup you need to hook up the cable that's going to control the
position of the choke plate that we saw
earlier on the choke horn of the body with an electric choke setup
the position of the choke plate is controlled automatically when the engine
is started
and then returns by itself to its closed position
when the engines off that'll cover most of the details for a Holley 4150
mechanical secondary carburetor let's move on