Maximum
performance cannot be achieved unless the carburetor is wide open when the
throttle is pushed to the floor. Consequently, throttle opening should be
checked regularly, immediately following any major changes in the engine
compartment. Maximum airflow cannot be achieved if the throttle plates do not
reach the wide-open position, or if it is pulled past wide open. The throttle
linkage should operate smoothly without binding and should be free of
obstructions that may cause the carburetor to stick open. An auxiliary return
spring MUST always be installed to insure that the throttle positively closes.
It may be necessary to install a stop to prevent the carburetor from being
opened too far and to prevent damage to the linkage. Take your time and set the
linkage up right! Tuning linkage on sideways mounted tunnel ram carbs will
take longer than a single 4 barrel.
Climate
Changes and Performance
Changes
in air density due to changes in temperature, barometric pressure, and humidity
will have a direct impact on engine performance. As the air density changes,
adjustments to the fuel mixture are often necessary. These factors can change
from afternoon to evening. Everyone knows the engine will make more power at
night when the air cools. The cooler, denser air carries more oxygen per cubic
foot and thus support the capacity to burn more fuel. The weather conditions
may not change enough from afternoon to evening to require mixture adjustments,
but adjustments will certainly be necessary as the seasons change. Traveling to
tracks in different climates or at different altitudes may also cause a need
for fuel mixture adjustments. These factors cannot be overlooked when tuning
for best performance.
Tuning
With Spacers
Spacers
and plenum dividers provide an easy way to change the configuration and the
characteristics of the intake tract and the relationship it has with the
carburetor. Adding a plenum divider to an open plenum manifold can help keep
the left to right fuel distribution balanced for oval track applications This
is especially helpful on alcohol engines.
Using
spacers between the carburetor and intake manifold can produce dramatic
results. The use of a four-hole spacer can improve low end to mid-range by
helping the carburetor draw and atomize fuel. An open center spacer increases
the plenum area and can benefit the mid-range and upper rpm power. It is not
uncommon to see combinations of spacer types or stacking of similar type
spacers being used.
The
actual results from any spacer or combination of spacers can only be measured
during a test and tune session on the specific engine combination being run.
This information can be a very useful tool when tuning to find the best
horsepower or to change the power characteristics to suit a specific track
condition.
Routine
Maintenance
For
consistent performance, a carburetor must be kept clean. Spray the air bleeds
with carburetor spray or WD-40 every week. Air bleeds become clogged from dirt
and dyes in the fuel. Clogged or dirty air bleeds can cause a stumble or a
high- speed miss in an otherwise perfect carburetor. If you are putting the car
up for the winter, use this little trick. Spin the engine over with the
ignition off and the throttle open and spray of WD-40 liberally down the
venturi will leave a fine mist of protection on the valve seats and cylinders
to prevent rust. Finally, your carburetor should be rebuilt at least once a
year and more frequently if itýs operated in dirty conditions.
Alcohol
Tips
Applications
running alcohol require additional maintenance beyond that of a gasoline fuel
system. Alcohol, being extremely corrosive, should not be left in the fuel
system or carburetor for an extended period of time. Proper care includes
draining and flushing the entire fuel system, usually with gasoline. The most
common method is to drain the system and add gasoline to the fuel cell allowing
the pump to draw fuel through the lines and to the carburetor. Alcohol
carburetors are much richer than gasoline, so when the engine begins to idle
and die, the system is pretty well flushed. If your sanctioning body allows the
use of fuel additives
, always use an additive that lubricates the fuel system
for protection while racing.
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