By: Henry P. Olsen
Continued
from Part 1: Fine Tuning the Fuel System.
In
part one of this tuning a carbureted engine
technical article we showed why and how
we tuned the ignition system of an engine
to perform its best with the unleaded reformulated
gasoline of today. The street rod we are
using to demonstrate our tuning techniques
is a Roy Brizio built 1936 Ford with a Roush
Performance 427 R engine that is rated at
550hp, but these same tuning techniques
will work on any carbureted engine. The
first step in the tuning process, after
we determined that the engine was mechanically
sound, was the fine-tuning of the ignition
timing (the initial timing as well as the
mechanical advance curve and vacuum advance
if used). Now with the ignition spark timing
optimized for today’s unleaded reformulated
gasoline, we will now proceed to the next
step, which is tuning the fuel system. We
will now show you the modern tools we use
to “read” the air/fuel mixture that the
carburetor is supplying the engine and how
we use these modern tools to tune the fuel
system so the engine can perform at its
best. We will first explain the tuning process
we use to tune the air/fuel and then show
how we apply this process to the engine
in the Roy Brizio built 36 Ford street rod
we are working on.
The
Air/Fuel Mixture
The
leaded gasolines that most carbureted engines
were designed to use allowed the engine
to perform very good even if the ignition
spark timing or the air/fuel mixture was
not properly tuned. The same cannot be said
for the unleaded reformulated gasoline of
today, unless the ignition spark timing
and the air/fuel mixture are properly tuned,
the engine will not perform like it should.
Most people think their engine is running
too rich because the exhaust fumes burn
their eyes; this is not true. An engine
with a rich air/fuel mixture will have excessive
carbon monoxide (CO) in the exhaust; carbon
monoxide is an odorless gas that is quite
deadly if you breathe too much of it. A
engine that has a misfire from things such
as: a rich air/fuel mixture, a lean air/fuel
mixture or incorrect ignition spark timing
will have a lot of unburned hydrocarbons
(HC) in the exhaust. Exhaust gas with a
high unburned hydrocarbon (HC) content will
burn your eyes and make it difficult to
breathe.
Back in the
days of leaded gasoline an experienced tuner
could attempt to tune the carburetors jetting
by reading the color the fuel left on the
insulator of
the spark plug. The unleaded reformulated
gasoline we have today has made the reading
of a spark plug almost impossible because
it leaves little or no color on the spark
plug insulator. If the engine is expected
to run its best, the fuel system must supply
the correct air/fuel mixture to the engine
for every driving condition. A engine tuned
with the correct air/fuel mixture for all
driving conditions will allow you to get all
the horsepower from your engine while getting
the best fuel economy.
A lean fuel mixture
(too little fuel for the amount of air in
the cylinder) can cause an engine to have
a surge or miss at idle and part throttle,
stumble on acceleration, lead to engine
overheating and cause a lack of power. A
rich air/fuel mixture (too much fuel for
the amount of air in the cylinder) can cause
an engine to “load up” at idle, foul the
spark plugs, and also lack power or run
sluggish.
Methods
for Reading the Air/Fuel Mixture
A
carburetor equipped street rod engine can
be tuned to run as well or even better than
it would have run with leaded gasoline by
using modern tools such an exhaust gas analyzer
to tune the engine. In the past, tuning
a fuel system to supply an engine with the
correct air/fuel mixture has always been
a task that almost impossible for most tuners.
A tuner had to attempt to tune the engine
by looking at the spark plug, the exhaust
port and the first 6 inches of the header
for proper “color” and then make a guess
at what air/fuel mixture change was needed.
Tuners can now use the new, more scientific
- modern method for checking the air/fuel
mixture with tools such as an infrared exhaust
gas analyzer and/or an extended range oxygen
sensor based air/fuel ratio meter. This
new technology analyzes the engines exhaust
content to allow you can “read” what air/fuel
mixture the engine is getting from the carburetor(s)
at any rpm and load condition.
The new advances
in exhaust gas analysis technology and wideband
oxygen sensor technology have made it possible
to “read” what the air/fuel mixture actually
is under almost any driving
condition. In the past exhaust gas
analyzers have tended to be large and expensive,
but the computer age has allowed the production
of many new units that are not only compact
and portable, but also affordable. Modern
technology has also made it possible to
use a wideband oxygen senor to “read” the
air/fuel mixture with a digital air/fuel
meter at an affordable price.
The
easiest and most accurate method that we
have found is using an infrared exhaust
gas analyzer. An exhaust gas analyzer “looks”
at the content of exhaust gases and then
supplies readings that can indicate what
the air/fuel mixture is and the efficiency
of the engine. The infrared exhaust gas
analyzer allows a tuner to “read” and record
for future reference what air/fuel mixture
is at any operating condition such as idle,
cruise speeds or wide open throttle, the
air/fuel mixture can be tailored to what
your engine needs to perform at its best.
The CO2 and NOx readings from the exhaust
gas analyzer can be used as a method to
determine if the ignition timing is correct
for what the engine needs for maximum power
and efficiency.
The
air/fuel mixture can also be checked by
the use of a wideband oxygen sensor installed
into the exhaust header, the sensor is “read”
by a digital air/fuel meter. This method
determines the air/fuel mixture by looking
at the oxygen/unburned combustibles in the
engines exhaust; the readings can be very
accurate, but false readings can be created
by a exhaust leak, engine misfire, or a
high overlap cam at lower engine speeds
(these false readings are caused by the
oxygen sensor misreading the extra oxygen
in the exhaust that is there because of
a misfire, an exhaust leak or the high overlap
cam).
The
original equipment carburetor(s) that are
on many street rod engines were not designed
or tuned for today's unleaded reformulated
gasoline, so in most cases the engine will
tend to run lean. The high performance and
replacement carburetors sold today are built
with a generic air/fuel mixture curve. These
aftermarket carburetors should be designed
with an air/fuel mixture that is rich enough
for a wide variety of engines packages with
different exhaust systems, but this is not
often the case. Most of the aftermarket
carburetors we see need a lot of tuning
work to get the air/fuel mixture correct
for the engines needs. The performance replacement
carburetors we prefer from our engine tuners
point of view are the part #1806 650 cfm
Thunder carburetor from Edelbrock or any
of the Mighty Demon carburetors from Barry
Grant Inc. The #1806 Thunder carburetor
works very well on a mild engine package
with a driver that uses his or her street
rod as a cruiser. When the driver is more
aggressive or has a high performance engine
with the goal of getting the maximum power
from their Street Rod we prefer to work
with the Mighty Demon series of carburetors
from Barry Grant. When you are using a race-designed
carburetor such as a Mighty Demon we always
suggest that the customer select a smaller
cfm most carburetor selection guides will
recommend. A larger cfm (air-flow) carburetor
will give you a little more high rpm power
at the expense of low and mid range power
and drivability, so unless you are always
driving at very high speeds at maximum rpm
your engine will perform better with a smaller
carburetor!
The
Barry Grant Mighty Demon carburetors have
changeable air bleeds, which make it easy
for a tuner to tailor the air/fuel mixture
for the engines needs. The new Demon six-shooter
3x2 bbl carburetor & manifold packages
that Barry Grant has for both small and
big block Chevrolet engines (Pontiac and
Ford packages are the next to come) promise
to be great package that will combine good
looks with lots of power. A modern 3x2 bbl
carburetor & manifold package such as
the new Demon six-shooter can allow an engine
to get good fuel mileage if you are light
on the throttle and keep your foot out of
the two outer carburetors.
Jetting
With a Infrared Gas Analyzer or Wideband
Oxygen Sensor
The
most accurate and easiest way to check the
jetting (air/fuel mixture) of an engine
is by observing the CO reading from an infrared
gas analyzer and/or a wideband oxygen sensor.
First place the sample probe into the tailpipe
and then the unit will “read” the exhaust
and supply the readings necessary to determine
the air/fuel mixture. The infrared exhaust
gas analyzer and/or the wideband oxygen
sensor method allows the part throttle air/fuel
mixture to be checked which otherwise is
almost impossible, the readings from either
method can be read in real time or recorded
and later played back. It is important to
note that any changes other than jet changes
and other basic adjustments should be done
by a proficient “carburetor expert” to avoid
damaging a #’s matching original carburetor.
A
starting point for air/fuel mixtures for
most mild performance engines is:
Idle:
1.0% to 3.0 % CO or a 14.1-13.4 to 1 air/fuel
mixture
Cruise
rpm: 1.0% CO or a 14.1 to 1 air/fuel mixture
with a mild performance engine: 1.0% - 3.0%
CO or a 14.1 – 13.4 to 1 air/fuel mixture
for a engine with a high performance cam.
Note: a 0% CO or 14.7 to 1 cruise air/fuel
mixture is chemically ideal but most high
performance carburetor equipped engines
will suffer misfire and drivability problems
when operated that lean.
Power
mixture and acceleration: 6.0% CO or a 12.5
to 1 air/fuel mixture for a “normal” engine;
a high performance engine with improved
combustion chamber design such as a Pro-Stock
or a Winston Cup engine, in some cases may
be able to use a slightly leaner power mixture
of 4% CO or a 13.0 to 1 air/fuel ratio.
Tuning
the air/fuel mixture with a infrared exhaust
gas analyzer
The
reading from an infrared exhaust gas analyzer
will indicate air/fuel ratio, engine misfire,
engine combustion efficiency and excessive
combustion chamber heat (detonation) by looking
at the following exhaust gases:
CO
(carbon monoxide): The reading from an infrared
gas analyzer is the reading that we use
to determine the air to fuel ratio. (Note:
CO is partially burned fuel.)
The
other readings that exhaust analyzers provide
are:
HC
(hydrocarbons): The amount of unburned fuel
or an indicator of an engine misfire, the
best mixture gives you the lowest HC.
CO2
(carbon dioxide): The product of complete
combustion, the best air/fuel mixture gives
you the highest CO2 reading. The ideal ignition-timing
advance will also create the highest CO2
reading
O2
(oxygen): A high O2 reading indicates a
lean mixture; an exhaust leak or the engine
has a “hot” cam. Note: if O2 is above 2
to 3%, the CO readings may not be accurate.
NOx
(oxides of nitrogen): A gas created by excessive
combustion chamber heat. In many cases a
high NOx reading may be related to excessive
ignition spark advance. The excessive spark
advance can cause engine ping or detonation
that can result in engine damage.
Fuel
Pressure and Volume
The
fuel supply system must supply enough fuel
volume with the correct fuel pressure at
every operating condition from idle to wide-open
throttle! The fuel pressure that we recommend
is 5-½ to 6-½ psi, if you increase engine
power you may need to install a high volume
fuel pump and increase the fuel line diameter
to avoid starving the engine. The fuel pressure
most not drop below 5 ½ psi at all engine
operating speeds or the carburetor float
level will drop and cause the carburetors
air/fuel mixture to lean out. For every
gallon of fuel the fuel pump pulls from
the gas tank and supplies to the carburetor,
one gallon of air must go into the gas tank.
If the fuel tank is not properly vented,
the fuel pump will be fighting against a
vacuum build up in the fuel tank, this will
cause the fuel pump not be able to supply
the carburetor with enough fuel pressure
and volume to feed the engines demands.
The fuel system that would supply the fuel
to an engine that could power a car to a
10 second run at a ¼ mile drag strip would
need to be able to fill a 1 gallon gas can
in under 25 seconds. If you run the engine
to long without enough fuel pressure and/or
fuel volume the air/fuel mixture will go
lean and then the results could be a burnt
piston or other engine damage.
Tuning
For Fuel Economy
The
fuel economy an engine can supply you with
will be its best when the air/fuel mixture
is at or near 14.7 to 1 a/f mixture, but
a carbureted engine may not perform very
well when the a/f mixture is that lean.
Many carbureted engine will run lack power,
misfire and/or run hot when you use a 14.7
to 1 a/f mixture so the engine will need
to be tuned for the a/f mixture that works
best for that engine package. The way we
tune a carbureted engine to find what the
ideal air/fuel mixture (read as CO) is for
gas mileage is the use of an exhaust gas
analyzer. When the an engine has the ideal
a/f mixture, it will burn all the oxygen
(O2) in the cylinder, create the lowest
amount of engine misfire (HC) and the ideal
air/fuel mixture will also cause the engine
efficiency (CO2) to be at it’s highest.
The best a/f mixture for gas mileage is
slightly on the rich side of where engine
misfire rate starts to rise. When you tune
the engine for maximum fuel economy the
power and drivability that an engine makes
will suffer. When you tune the engine for
maximum power and drivability the engine
will burn more fuel, but a good tuner can
supply you with both good fuel mileage and
good power/drivability.
Tuning
the power system opening point can also
be used to increase gas mileage. As you
tune the power system to open at a lower
vacuum it will take more throttle opening
to get the richer power mixture to kick
in. If you have a carburetor with a power
valve, you can change to a power valve that
opens at 4.5 inches of vacuum instead of
8.5 inches of vacuum. A carburetor that
uses a power piston and metering rods power
system opening point can be modified to
open later by changing the power piston
spring to a lighter spring rate.
Proper
ignition timing and advance curves must
be used if you expect the engine to burn
the a/f mixture at the correct time, making
the power that pushes the piston down in
the cylinder. A high NOx reading from an
exhaust gas analyzer indicates that the
ignition spark advance may be excessive
for the fuel you are using, so the NOx reading
from an exhaust gas analyzer can also be
used as an ignition spark timing tuning
aid.
Tuning
with a Wideband Oxygen Sensor
The wideband
oxygen sensor looks at the unburned combustible
content in the exhaust and the air/fuel
meter converts its signal into an air/fuel
mixture reading. This method requires you
to know what air/fuel mixture your engine
needs for each driving condition, this data
should be available from your engine builder
or you can use a infrared exhaust gas analyzer
to help you determine what air/fuel mixture
your engine needs to run its best. An extended
range oxygen sensor can “read” air/fuel
mixtures as rich as 9 to 1 and it can read
air/fuel mixtures as lean as 19 to 1 (a
standard oxygen sensor is only accurate
at air/fuel mixtures of around 14.7 to 1).
This method has the advantage of extremely
fast reaction times for the readings, but
false lean readings can be created under
certain operating conditions. The false
readings are created when the oxygen sensor
“sees” the excessive oxygen in the exhaust
system that can come from a engine misfire,
a supercharged engines “blow-thru” effect
(at low engine speeds), a high performance
camshaft’s valve overlap or an exhaust leak.
The
wideband oxygen sensor based air/fuel meter
that we use is the LM-1 Digital Air/Fuel
Meter from Innovate Motorsports, this unit
can allow you to sample and record the air/fuel
mixture data at a rate of 12 samples per
second over a period of up to 44 minutes,
this data can allow you to “read” the fuel
mixture the engine is getting and then confirm
the tuning changes you make give you the
fuel mixture you are targeting.
When we are
tuning a fuel system we use both the infrared
exhaust gas analyzer and the wideband oxygen
sensor methods, this way we can take advantage
of both tuning methods. The use of an infrared
exhaust gas analyzer, while slower in reaction
time, has the advantage that it not only
reads the oxygen/unburned combustibles content
of the exhaust like a wideband oxygen sensor,
but also allows you to determine the air/fuel
mixture by observing the CO reading (carbon
monoxide); the engine’s rate of misfire
can be determined by observing the HC reading
(hydrocarbon); the engine’s efficiency can
be determined by observing the CO2 reading
(carbon dioxide) reading. Spark knock, detonation
or engine ping that is in most cases is
caused by overly advanced ignition timing
can be seen by observing the NOx reading
(oxides of nitrogen).
Caption:
The above chart shows the gases in the exhaust
that an infrared exhaust gas analyzer reads
and how the gases change as the air/fuel
mixture changes.
Reading
the Air/Fuel Mixture
After
the basic engine condition and tune-up (fuel
pressure, timing curve, etc) is confirmed
to be correct, as well as checking to be
sure there are no vacuum leaks, the next
step is to determine what the air/fuel mixture
is at idle through 3000rpm. If the cruise
mixture is off, first change the jets in
order to get the air/fuel mixture correct
at the 2500-3000-cruise rpm range. Then
check and set the idle mixture. If the air/fuel
mixture is too lean at idle or part throttle
and the idle mixture screws do not provide
enough adjustment, the correction may involve
enlarging the idle “jet”. If the mixture
is still lean at 1000 through 1800 rpm,
the idle channel restriction on a Quadrajet
or the economizer restriction on a Carter
AFB (also the Edelbrock Performer or Thunder
series) may have to be slightly enlarged
to allow more fuel to be delivered at part
throttle. This lean condition at part throttle
condition will cause the engine to miss
or stumble on light acceleration and 15
– 30 mph light cruise speeds; this lean
off idle problem is also very common on
many of the performance replacement carburetors
sold today.
If
the air/fuel mixture is too rich at idle
and/or part throttle, the idle jet or part
throttle idle restriction may be too big
and may need to be replaced with a smaller
one. Once you have the idle, part throttle
and cruise air/fuel mixture curves correct,
the next step is a road test. A road test
using a portable infrared exhaust gas analyzer
and/or a wideband oxygen sensor will allow
you to check the cruise speed air/fuel mixture,
followed by a check of the power air/fuel
mixture under load. This type of test allows
you to see what the air/fuel mixture is
at the real world driving conditions you
will drive your street rod at, during this
road test you will be able to read and then
correct the air/fuel mixture. If you “see”
an air/fuel mixture reading that goes too
lean at high engine loads, the first thing
to do before you change jet size is to check
that the fuel pressure. The fuel pressure
must stay above 5 psi at wide-open throttle,
if not the carburetor will starve for fuel.
The low fuel pressure could be caused by
the fuel pump not having enough volume or
the fuel tank vent may not be letting enough
air into the tank to replace the fuel being
removed from it.
Tuning
The Carburetor
A
carburetor has an accelerator pump, idle,
main jets, and in most cases a power system
that is designed to supply the correct air/fuel
mixture for the engine’s demands. An idle
system will have an idle jet/restriction
that must be changed to supply the desired
fuel mixture for idle and off idle engine
demands. If your engine is equipped with
a Holley style carburetor (sold today by
both Holley and Barry Grant as the Demon
Series), the main jet size is what determines
what air/fuel mixture is delivered to the
engine at light load/cruise speeds (1500rpm
and up) and the power valve restriction
(under the power valve) is the determining
factor in what the air/fuel mixture the
carburetor will supply when the power valve
is open; a 6.5 inch power valve will be
open and supplying the richer air/fuel mixture
needed under high power demands anytime
the vacuum is below its 6.5 opening point.
A power valve has a reputation for being
a weak spot in this design of carburetors,
but the carburetor can be retrofitted with
backfire protection, which will help in
reliability. A carburetor that uses metering
rods in the primary jets such as a Quadrajet
or Carter AFB (sold today by Edelbrock today
as the Performer and Thunder Series) will
use the metering rods to change the air/fuel
ratio for both the power and cruise mixture
demands of the engine; the larger the metering
rod diameter the leaner the air/fuel mixture
will be.
The
accelerator pump system adds fuel as the
throttle valves are opened, tuning the accelerator
pump squirter volume and duration it’s tuning
is mainly done by trial and error in-order
to obtain the best throttle response, but
a 12.5 to 1 air/fuel mixture is a good place
to start. The problem we most often see
on a engine with a Holley carburetor is
a hesitation on quick acceleration, the
cure we use for this is to install an accelerator
pump upgrade kit part #1330 that we get
from Ole’s Auto Parts, the pump upgrade
kit makes the accelerator squirt more active.
We also use an improved accelerator pump
on the Edelbrock Performer (also know as
a Carter AFB) & Thunder (Carter AVS)
carburetors to make the pump more active
and help avoid hesitation problems on acceleration.
We buy the fuel system tuning parts we need
from Ole’s Auto Parts, they have the accelerator
pump upgrade kit we use for Holley carburetors
(Ole’s part #1330) and an improved accelerator
pump (Ole’s part #1010) for Edelbrock Thunder
& Performer carburetors and the 9000
series AFB carburetors that Carter sold.
Tuning
the fuel system in the 36 Ford
Now
it is time to check out the air/fuel mixture
the engine is getting from the carburetor,
but first we checked the fuel pressure and
confirmed it was at 6 ½ lbs. The next step
was to check the air/fuel mixture the engine
was getting by the use of our 5-gas exhaust
gas analyzer. The readings showed that the
air/fuel mixture was slightly lean at idle,
as we increased the engine speed the air/fuel
mixture the engine was getting from the
off-idle system was very lean and then at
about 3,000 rpm the air/fuel mixture the
engine was getting thru the main circuit
was much closer to the we would want to
see for a high performance engine such as
this. The exhaust gas analyzer also showed
us that the accelerator pump was very lazy
by the very lean readings we were getting
as we snapped the throttle for quick acceleration,
we could also hear the engine bog and try
to backfire thru the carburetor when we
snapped the throttle. The carburetor needed
the idle system modified to supply the engine
with a richer idle & off-idle air/fuel
mixture and the accelerator pump would need
a lot of help. The Holley carburetor also
was a vacuum secondary unit with a two corner
idle system, a engine with a big camshaft
and/or a air-gap intake manifold will perform
best with a carburetor with a four corner
idle circuit. We would also in most cases
prefer a carburetor with mechanical secondarys
so the driver can control when the secondarys
will open.
The
Roush 427R engine we are working on has
both a big camshaft and a single plane air/gap
style intake manifold. In general unless
you are building a race engine an air-gap
style intake manifold will not provide enough
extra power to make up for the tuning headaches
that come with this type of intake manifold.
A air-gap intake manifold can make more
power because the air-gap design cools the
incoming air/fuel charge, but when used
on the street the air charge can become
so cool that that the fuel and air do not
stay properly mixed together. When the air
& fuel are not mixed together properly
you will lose power and waste a lot of very
expensive gasoline. The intended driving
style for this very powerful engine is maximum
power, but since the main use of this 36
Ford street
rod is on the street and not at a racetrack
we recommended the intake manifold be changed
to a non air-gap dual plane Edelbrock Performer
RPM.
Rather
than put a lot of work into a carburetor
that is not very tuner friendly we decided
to install a 650 cfm Mighty Demon carburetor
with mechanical secondarys. The Mighty Demon
is designed for a high performance engine
such as this.It has a very responsive accelerator
pump system and can easily be tuned to supply
the richer air/fuel mixture that this high
performance engine will need because of
its air-gap style single plane intake manifold,
large intake ports and aggressive camshaft.
We installed the 650 cfm Mighty demon and
then adjusted the idle speed & air/fuel
mixture while observing the readings from
the 5-gas exhaust gas analyzer. The readings
we saw on the read out showed us the air/fuel
mixture was right on target as it came out
of the box and when we snapped the throttle
the engine responded instantly. The idle
air/fuel mixture the exhaust gas analyzer
showed us was at our target idle air/fuel
mixture of 3.0 % CO or 13.4 to 1 air/fuel
mixture that this engine idled best at,
the exhaust gas analyzer readings also showed
us that the air/fuel mixture was right on
the target air/fuel mixture of 3.0% CO or
a 13.4 to 1 air/fuel mixture at all engine
speeds thru 3000 rpm. When the throttle
was snapped the exhaust gas analyzer now
showed us that the Mighty Demon’s very responsive
accelerator pump system was supplying the
engine with the proper 6.6% CO or a 12 to
1 air/fuel mixture that is needed form the
accelerator pump system and now the throttle
response was much better and the engine
no longer had any hint of a backfire.
Now
it is time for the most important part of
the tuning process, the test drive. We mounted
the Innovate LM-1’s wideband oxygen sensor
in their unique tailpipe probe in the exhaust
pipe and now it is time for the test drive.
The LM-1 readings allows us to we observe
what the air/fuel mixture is in real time,
while the car is driven on the road under
real world driving conditions. The first
thing we both noticed was when the Roy
hit
the throttle it no longer hesitated, it
just pinned us in the back in the seats.
The power was very impressive but as the
engine rpm got above 4000 rpm the power
started to fade. The readings from the Innovate
Motorsports LM-1 showed us that the air/fuel
mixture was going very lean.
Back
at the shop we installed a fuel pressure
gauge and again went for a test drive. As
we again accelerated to 4000 rpm we noted
the fuel pressure was dropping from the
6-½ lbs we saw at the shop to below 2 lbs
at 4000 rpm. When we again got back to the
shop we found that the electric fuel pump
that was in the car was not a high enough
volume unit to supply the fuel need to produce
550 horsepower. We next installed a high
volume electric fuel pump along with larger
fuel lines to solve this problem. This time
on the test drive the engine accelerated
to 6000 rpm without a trace of problem,
the 36
Ford street
rod was now scary fast. The air/fuel mixture
readings on the Innovate LM-1 showed us
the air/fuel mixture was right on target
at every condition that Roy drove us at,
the cruise mixture was reading right at
the 13.4 to 1 air/fuel mixture that we use
for a high performance engine like this
427/550hp power plant. The readings the
LM-1 gave us also showed us that the power
system from the Mighty Demon carburetor
was supplying the correct air/fuel mixture
of 12.5 to 1 that an engine needs for maximum
power. As I looked at the air/fuel mixture
readings when the driver hit the throttle,
I noted the air/fuel mixture the accelerator
pump was supplying the engine went right
the 12.5 to 1 air/fuel it should have and
stayed there as long as driver stayed in
the throttle.
The
problems that were present when we started
this tuning story are no longer there, the
ping problem is gone, the hesitation when
the throttle is no longer present, the engine
now has almost unbelievable power thru 6000
rpm and beyond and the exhaust fumes that
were causing everybody’s eyes to burn is
much less noticeable. The ignition spark
advance curve and the air/fuel just had
to be tuned correctly for the engine and
the unleaded reformulated gasoline it will
be burning.
Taking
the time to properly tune your street rod’s
engine air/fuel mixture and ignition spark
advance will not only allow you to unlock
all the power that was built into the engine
while avoiding doing any damage to your
engine due to a incorrect fuel system tune
up or over advanced ignition timing. A properly
tune engine will also get the best fuel
mileage, with gasoline selling in the $2.00
to $3.00 a gallon range how can you afford
to drive any car or truck with a un-tuned
engine. For a more detailed explanation
of the use of a 5-gas infrared exhaust gas
analyzer in fuel system diagnosis on the
web go to: www.automotiveu.com.
Special thanks go out to the technical training
& engineering staff at OTC/SPX Corporation
as well the fine staffs at Bridge Analyzers,
Barry Grant Inc. and Innovate Motorsports
for their help, patience and input on the
methods we use to tune an engines fuel mixtures
and ignition advance systems with their
products. Their help and advice has made
it possible for us to explain to you how
we tune an engine to perform it’s best with
today’s unleaded reformulated gasoline!
Sources:
Ole’s
Carburetor & Electric, Inc.
Ole’s
Carburetor & Electric Inc.
120
El Camino Real
San
Bruno , CA 94066
650.589.7377
olescarb@sanbrunocable.com
John
Bishop/Hot Rod Tuning
Burlingame,
CA
Ph#650
343 4860
jfb396@sbcglobal.net
Demon
Carburetion
Barry
Grant, Inc.
706-864-8544
www.barrygrant.com
OTC/SPX
Corporation
1-800-533-6127
www.otctools.com
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