-18-

Power Enrichment Calibration

The power enrichment calibration of the 2V carburetor is not
considered adjustable since changes in calibration would require
internal modification. The parts required and special knowledge
is not readily available except to specialists.

The 1V carburetor also requires internal modifications to
change the calibration. This is a metering rod carburetor requir-
ing changes in parts and internal dimensional settings not nor-
mally available to the general public. In summary, this is not

judged an adjustable parameter.


-12-

Impact on servicing costs and quality - As previously pointed
out, in normal use, there is a need, due to changing engine condi-
tions, to re-adjust idle mixture to maintain adequate idle quality.
Idle quality problems such as stalling and roughness are readily
apparent to the driver and are problems he will seek to have cor-
rected. Although the source of the problem may not be carburetor
related, the job of finding these non-carburetor problems is often
difficult, time consuming, and consequently, costly. If the pro-
blem is a minor induction system leak, the problem can be corrected
by carburetor mixture adjustment. Lacking a mixture adjustment,
there may be a tendency to recommend a replacement carburetor.

This can involve a cost of $25 to $53 plus labor, without correct-
ing the problem. If the problem was carburetor deposit related, it
would have corrected the problem, however, depending upon the ex-
tent of the deposit, a mixture adjustment could correct the idle
quality complaint at lower cost. Warranty costs, we project, would
increase due to lack of means for the dealer to correct a common
complaint, however, there is no data available for the writer's
determination of the magnitude of this increase.

Extensive field studies of vehicles in service are required
to identify the problems that may be created by the elimination of
idle mixture adjustment and to evaluate the performance of non-
adjustable idle systems.

The closed loop exhaust sensor - carburetor control systems pro-
posed for future emission control systems will not, at their cur-
rent state of development, alter the positions taken in the preceed-

ing on idle mixture adjustment.


~-22-

Although this is under study through CRC, a totally acceptable
test has not been developed.(2) To complete this development will

involve substantial cooperative work and testing.


Section 2

ScOPZ OF WORK

The purpose of this study is to determine the impact of an
crA regulation, targeted for the 1980 model year, which would re-
quire that carburetor adjustments be limited such that emission
data certification vehicles could meet emission standards regard-
less of carburetor adjustment settings. ‘The carburetor parameters
to be considered are:

1. Idle mixture

‘2. Idle speed (minimum speed)

3. Choke bi-metal setting

4, Choke vacuum break setting

5. Accelerator pump quantity
€, Fower enrichment calibration

?. ¥Yart throttle calibration
‘whe impacts to be determined on the manufacturers and the purchaser/
owner are:

1. iianufacturing lead time

2, Criginal equipment manufacturer (U.u.N.) costs

3. Service costs and quality

4, warranty costs

5. In-use problems


-19=

Part Throttle Calibration

The calibration of the 2V carburetor can be changed by jet
replacement; this is an internal part. On the 1V carburetor, a
metering rod change or a change in the metering rod operating pos-
ition will alter the part throttle calibration. We do not consider
this an adjustable parameter in either of the carburetors under
consideration, To change the design of either of these carbure-
tors to accomplish 100% assurance that the calibration could not
be changed by a specialist through carburetor tear down and modi-
fication cannot be visualized by the writer at this time. If it

is possible, we would not consider it feasible in the time frame

proposed for this regulation.


~25-

increase due to a possible increase in the sale of replacement

bi-metal assemblies in lieu of ability to adjust.

Choke break setting - This is not considered an adjust-
ment on the 1V carburetor under study and would not be in-
cluded in the proposed regulation. This is an internal ad-
justment required during carburetor manufacture and at car-
buretor rebuild to bring the carburetor to proper specifica-
tions. On the 2V carburetor, it is an external adjustment

which can be eliminated by redesign.

Accelerator pump quantity - On the 2V carburetor under
study, this is an external adjustment and could be eliminated.
On the 1V carburetor under study, it is not an external ad-

justment and should not be affected by the proposed regulation.

Power enrichment calibration - Not an external adjust-
ment on either carburetor involved; should not be affected

by the proposed regulation.

Part throttle calibration - Not an external adjustment
on either carburetor; should not be affected by the proposed

regulation.


-21-

available gasoline additives. The reports have shown that without
an effective additive, the deposits cause idle mixture and the low
end of the part throttle calibration to become richer, adversely
affecting idle quality, fuel economy, and exhaust emissions, It
may be desirable to repeat some of the work on current or advanced
carburetor systems. Although the degree of the effects of additives
reported to date may be debated, the trend is unmistakable.

There are gasolines sold today that do not have an effective
carburetor additive. This acts to reduce the quality of idle which,
in turn, will call for more frequent engine tune up, specifically
idle mixture adjustment.

Effective carburetor additives exist today and could be made
available in unleaded gasoline sold in 1980 given proper incentive.
The writer estimates the added cost to a gallon of gasoline would
fall in a range from 0.1¢ to 0.3¢. The writer is not in a position
to estimate the capital costs involved.

Certain of the additives available are effective in control-
ling intake manifold deposits. These deposits, if present in
sufficient quantity, adversely affect driveability.

In considering carburetor or total induction system additives,
the need for developing a practical performance evaluation test
that correlates with field performance becomes a necessity. A
concern in developing the performance evaluation test is the need
to recognize changing emission control system designs and possible

effects on the prior established performance of an additive.


~16-

Ghoke Vacuum Break Setting

The 2V carburetor under consideration has an external adjust-
ment of the choke vacuum break setting. This could be redesigned
at approximately 10¢ increase in piece cost and available for 1980
model year production. Tooling costs should not exceed $40,000,
Again, these are the writer's estimates in advance of final design.

The extent to which this adjustment is needed and used in ser-
vice is difficult to determine, therefore, the impact on servicing
quality and costs is difficult to estimate. In the interest of
maintaining the manufacturers' specifications and preventing mis-
adjustment in use, there is reason to eliminate this external ad-
justment.

The 1V carburetor under study does not have an external ad-
justment of vacuum break setting, and by the writer's definition,
requires no change in this area to meet the intent of the proposed
regulation. Setting the choke to specification during manufacture
of the carburetor is accomplished by bending the internal linkage.
Without major redesign of the carburetor, we know of no means to
assemble the carburetor without some means of adjustment to speci-

fications during assembly.


Section 6

IMPACT OF THE PROPOSED REGULATION

In this section the contractor addresses each of the seven
carburetor parameters that are listed in the Scope of Work in
terms of the five impacts listed.

The issue of carburetor deposits and the effects of gasoline
additives will be covered in a separate discussion.

A summary including the contractor's recommendations will

conclude the report.

Idle Mixture

Design and manufacturing - On the 1V and staged 2V carbure-
tors under discussion, the current 1977 carburetor designs have
mixture adjustments and the adjustment range is limited by a plas-
tic cap. The limits could be exceeded, however, by the use of
excessive force with available hand tools. In all probability,
the emission standards could not be achieved at the maximum range
of the adjustment achieved in this manner. A redesign is required
to meet the requirements of the proposed regulation.

To meet the requirements of the regulation would require eli-
mination of the external mixture adjustment at the time the carbur-
etor is shipped from the carburetor manufacturer. The design to
be employed on both the 1V and the staged 2V carburetor could be
a hardened steel cup plug or plate pressed into the carburetor
body covering the idle mixture screw. The idle mixture screw

would be available during the manufacture of the carburetor.


Section 4

RATIONAL AND APPROACH

The assessment of the impact of the proposed regulation as
outlined in the Scope of Work is addressed from the view point of
a Chief Engineer of a typical automobile manufacturer; however, it
is not an assessment of the impact on the total automobile indus-
try. Discussion is limited to two carburetor types, a 1V and a
staged 2V, as would be used on 4 or 6 cylinder engines in compact
cars. Although the carburetors selected are currently in produc-
tion and scheduled for 1980, the study is not intended to cover
the great diversity of carburetors currently in production or
scheduled for production in 1980. As a point of reference, we are
considering a total annual volume of 400,000 cars.

Included in the study is consideration of the impact on engi-
neering, manufacturing, sale, and owner satisfaction with the ve-
hicle throughout its useful life which is considered 10 years and
100,000 miles. Proper servicing and overall performance of the
vehicle is of great importance since it reflects on repeat sales
and the overall public image of the manufacturer.

The study does not provide detailed design information on
means of meeting the requirements of the regulation although it
will reference design concepts. Detailed projections on the af-
fect of the’ proposed regulation on warranty costs or servicing
costs over the life of the vehicle are not provided since the
basic information required is not available at this time.

Although the contractor had meetings with carburetor suppliers,


Section 3
CONTRACTOR'S INTERPRETATION OF Wie KRe&GULATION
REFER“NCED IN THE INTENT TG DEVELOP RULENAKING
FUBLISHZD IN FEDERAL REGISTER VOL. 42, NO. 104
DATED MAY 31, 1977
Understanding of the regulation is based on preliminary meet-
ings discussed in Section 1. Definition and clarification of two
basic questions are required when addressing this study and meet-
ing the objective as described in the Scope of work. ‘The two
questions are:
1. «hat is an adjustment?
, 2. what defines the limits of an adjustment?
‘fhe contractor (Cc. #. Burke) defines an adjustment as a means
external to the carburetor capable of changing tne calibration of

a parameter and accessabdle without dissassembly of the carburetor.

‘he limits of an adjustment are defined as the maximum change

that can be made toward either extreme, intentionally or uninten-
tionally, either by hand or using normally available hane tools

such as screw drivers, socket wrenches or slicrs.


17-

Accelerator Pump Quantity
In the case of the 2V carburetor under consideration, accel-

erator pump quantity is externally adjustable. This adjustment
could be eliminated by the 1980 model year. No change in piece
cost would result with minimal tooling cost involved.

The extent to which changes in pump quantity (pump stroke) is
used in service is not clearly defined, but it is the writer's
judgment that it is minimal. There may be some advantage from a
driveability standpoint to move from the mean pump adjustment to
prevent "slugging" at high ambient temperatures and improve warm
up driving at cold ambients, however, it is the writer's judgment
that the need is minimal.

In the case of the 1V carburetor under consideration, no ex-
ternal adjustment is available. The internal changes required to
change the pump quantity involve changes in springs, shims, or
plugging of a by-pass hole, if one is used in the calibration. The
information required to make a change is only available to carbure-
tor specialists. We do not judge the proposed regulation will af-

fect this carburetor in the pump area.


Section 5
ORGANIZATIONS CONTACTED
Cardo Automotive Products, Inc.
Fhiladelphia, Pennsylvania

Carter Carburetor Division, ACF Industries
St. Louis, Missouri

Champion farts Rebuilders, Inc.
Gak Brook, Illinois

Chevron Chemical Company, Oronite Additives
San Francisco, California

Chevron Research Company
Kichmond, California

nyl Corporation, Research Laboratories
Detroit, kichigan

siolley Carburetor Division, Colt Industries
warren, i.ichigan

mobil Research and Development Corporation
Paulsboro, itew Jersey

Furpose of meetings: 1. To contact normal carburetor sup-
pliers and discuss action to be taken in regard to the proposed
regulation. ‘nis is the normal course of action of a Chicf ungi-
neer. 2, To contact other organizations who may have information

mn the impact of the regulation, esnecially as it affects the ner-

formance of the manufacturers' vehicles after sale.


-23-

Section 8

SUMMARY AND RECOMMENDATIONS

The proposed regulation, as presented to the contractor, has
the objective to limit carburetor external adjustability. In addi-
tion, certain parameter adjustments were included which are con-
trolled by internal components. On those occasions that carbure-
tors are disassembled for service and replacement of parts, it is
necessary on reassembly to make certain internal adjustments to
compensate for slight dimensional differences in the new parts to
bring the total carburetor assembly to original manufacturing spec-
ifications. To accomplish this, the carburetor design must pro-
vide this adjustability.

It is the contractor's estimate that during the life of the
vehicle the carburetor must be disassembled for service at least
once and possibly several times.

The carburetor rebuilding and replacement industry, as cur-
rently constituted, has the same need as the original manufacturer:
to make internal adjustments to assembled specifications. As an
indication of the extent of carburetor servicing and replacement
during the life of the vehicle, it has been estimated that the
total carburetor replacement industry produces nearly 10,000,000
units annually. Their major volumes are for cars five and six
years old.

The carburetor is often subject to adjustment, tear down, or
replacement as a result of misdiagnosis of driveability problems.

Proven diagnostic techniques and equipment should be developed and


EPA-420-S-77-101

ASSESSMENT OF A PROPOSED EPA REGULATION WHICH
WOULD REDUCE CARBURETOR ADJUSTABILITY

(Ref. - Intent to Develop Rulemaking by EPA,
New Motor Vehicle Certification, Federal Reg-
ister, Vol. 42, No. 104, Tuesday, May 31, 1977)

For: The Environmental Protection Agency
OAWM, MSAPC
Ann Arbor, Michigan
Order No. CD-7-0152-A
Michael W. Leiferman, Project Officer

By: C. E. Burke Engineering Services
11035 Auburndale
Livonia, Michigan 48150

August 13, 1977

This report was furnished to the Environmental Protection
Agency by C. E. Burke Engineering Services, 11035 Auburndale,
Livonia, Michigan 48150, in fulfillment of Service Order

No. CD-7-0152-A. The contents of this report are reproduced
herein as received from C. E. Burke Engineering Services.

The opinions, finding, and conclusions expressed are those
of the author and not necessarily those of the Environmental
Protection Agency. Mention of company or product names is
not to be considered as an endorsement by the Environmental
Protection Agency.


-10-

would not be available. In many cases, however, this would not
correct the driveability problem, and it would result in a high
rate of return of replacement carburetors with its consequent neg-
ative impact on the business. This situation would be relieved to
some extent if a means to adjust mixture in service was developed
and incorporated in the design which was not as readily accessible
as is the case in current external adjustments.

Mixture adjustment has been available and required in vehi-
cles since the introduction of mass-produced automobiles. The
limiter caps installed on current vehicles still allow for adjust-
ment when the need arises although, admittedly, this has been
abused from the standpoint of emission control.

Circumstances that call for mixture adjustment and potential
impacts of its elimination are:

1. Induction system leaks develop in vehicles in use at
the many gasketed joints and hose connections during the nor-
mal life of the vehicle. When minor leaks develop and before
they are readily detectible, a mixture adjustment is required.
It can be assumed that the potential for induction leaks can
be reduced by improved design and material. The cost and
lead time for this is not known because the extent of the pro-
blem has not been identified. The emission control system
includes many calibrated air flows which are flowing into the
induction system at idle and are included in the original mix-
ture setting calibration. These fixed flows include PCV,

choke heat air, evaporative control system, and others. When


-9-

This new design could be made available for 1980 model year pro-
duction. The calibration of the fixed mixture setting would be
that required to meet emission certification.

Costs of the non-adjustable mixture designs on the two car-
buretors under consideration would not be available from the car-
buretor suppliers since the final designs would not be resolved
at this point. The contractor's broad estimate of the cost in-
crease (customer cost in 1977 dollars) of the carburetor would be
15¢ to 25¢ with a range of tooling costs from $20,000 to $100,000.

Since mixture is not normally adjusted during vehicle manu-
facture, no significant impact would be felt during this process.

We are optimistic that certification can be accomplished
without mixture adjustment. Carburetors without caps, making the
mixture screws accessable, would be available during engineering
development and finalizing of emission control system specifica-_
tions.

We are concerned that a non-adjustable mixture in either car-
buretor would have serious impact on the performance of the vehi-
cles in use. Idle quality problems could not be adequately ser-
viced in all cases and would result in higher servicing costs dur-
ing the life of the vehicle. Aftermarket carburetor rebuilders
would, in all probability, produce replacement carburetors without
mixture adjustment since their policy is to match original equip-
ment carburetors. It can be projected that the sale of replace-
ment carburetors would increase since ready means to correct idle

mixture related driveability problems or non-complying emissions


-6-

representatives of the petroleum and fuel additive industries, and
replacement carburetor manufacturers for the purpose of expanding
his background in the technical areas affected, the views ex-

pressed are those of the contractor based on his judgment.


-20-

Section 7

CARBURETOR DEPOSITS

In normal operation using gasolines without a proper addi-
tive, deposits form in the carburetor and intake system of the
engine. The source of these deposits are atmospheric contami-
nants, engine blow-by, exhaust gas recirculation gases, and gaso-
line gums. These deposits accumulate in the throttle plate area
of the carburetor affecting idle mixture and consequently, idle
quality and raise idle emission of CO and HC. Deposits also ac-
cumulate in other areas of the carburetor such as at the air
pleeds affecting the overall calibration and in the choke area
which can affect choke performance. These deposits can accumulate
at relatively low mileage.

In the consideration of a regulation which would serve to
reduce carburetor adjustability, the subject of carburetor depos-
its is pertinant. Carburetor adjustability has served in the past
to adjust carburetor metering to changing engine conditions. De-
posit formation in the induction system is one of several engine
and carburetor changing conditions.

Considerable field testing has been done by the petroleum and
additive industries in past years which has documented the nature
and affects of induction system deposits.(1) This information has
been reported and is in the public record. Considerable work on
the performance of gasoline additives has been reported showing
that the induction system deposit ‘problem, particularly the car-

buretor deposit problem, can be effectively controlled by use of


(1)

(2)

-26-
REFERENCES

J. B. Retzloff, L. Plonsker, and R. B. Sneed, Ethyl Corpora-
tion Research Laboratories, Detroit, Michigan. "Fuel Deter-
gency - Effects on Emissions", presented at the National Fuels
and Lubricants Meeting, Tulsa, Oklahoma, October 31 - November
2, 1972.

K. L. Kipp, J. C. Ingamells, W. L. Richardson, and C. E. Davis,
Chevron Research Company, Richmond, California. "Ability of
Gasoline Additives to Clean Engine and Reduce Exhaust Emissions"
presented at the SAE Mid-Year Meeting, Detroit, Michigan, May
18 - 22, 1970. SAE Paper 700456.

Donald W. Houser, Richard F. Irwin, Louis J. Painter, and
George H. Amberg, Chevron Research Company, Richmond, Cali-
fornia. "Field Tests Show Gasoline Deposit Control Additives
Effective in Emission Reduction" presented at the 64th Amual
Meeting of the Air Pollution Control Association, Atlantic
City, New Jersey, June 27 - July 2, 1971.

D. H. Hall and L. M. Gibbs, Chevron Research Company, Richmond,
California. "Carburetor Deposits - Are Clean Throttle Bodies
Enough?" presented at the SAE Meeting, Dearborn, Michigan,
October 18 - 22, 1976. SAE Paper 760752.

L. M. Gibbs and N, F. Pereira, Chevron Research Company, Rich-
mond, California. "Does Unleaded Gasoline Need a Deposit Con-
trol Additive?" presented at the National Fuels and Lubricants
Meeting, Houston, Texas, September 13 - 14, 1973.

D. S. Orrin, W. R. Miner, and K. L. Kipp, Chevron Research
Company, Richmond, California. "Unleaded Gasoline - Lubri-
cant Requirements and Fuel Additive Performance" presented at
the SAE National West Coast Meeting, San Francisco, California,
August 21 - 24, 1972. SAE Paper 720689.

Carburetor Test Procedure Panel of the Coordinating Research
Council Motor Fuels and Engine Cleanliness Group. (Coor-
dinating Research Council, Inc., 30 Rockefeller Plaza, New
York, New York 10020).


Section 1

PRELIMINARY MeeTINGS

On March 10, 1977, C. E, Burke of C. &. Burke Engineering
Services met with John P. Dekany, Division Director of the mnvi-
ronmental Protection Agency mission Control Technology Division,
and Charles Gray and Karl Hellman of his staff in Ann Arbor, iich-
igan. ‘The purpose of the meeting was to outline the objectives
and other details of the request by EPA for a study of a regula-
tion PA planned to propose which would, in effect, reduce car-
buretor adjustability. Other meetings and discussions were sub-
sequently held to develop the details of this request.

It was agreed that for the purposes of submitting his bid,
the writer would consider the proposed regulation to require cer-
tification vehicles for the 19&0 model year to meet emission stand-
ards with any or all of tne carburetor adjustments affecting seven
carburetor parameters set at any point within the available adjust-
ment range or at any missadjustment which could be accomplished
using normally available hand tools.

The writer submitted the bid of C. &. Eurke imgineering Ser-
vices in a letter to John ¥. Dekany dated April 4, 1977 which was
subsequently accepted. Service order CD-7-0152-A, provided to
Cc. #. Burke ingineering Services, authorized the work herewith

resorted.


-13-

Idle Speed (Minimum)

Design and manufacturing - Idle speed is adjustable on the
two carburetors under consideration. If we set aside, for the mo-
ment, other problems, it can be said that a design which sets a
low limit to idle speed could be tooled and produced for the 1980
model year, The detail of the design is not available, but if it
consisted of an additional idle stop screw, covered or eliminated
after setting on the carburetor flow box, the added cost per car-
buretor could reach 20¢ with a tooling cost of $50,000.

. The design would have no direct effect on the process of ve-
hicle manufacture although idle speed problems that would come up
as a result of this design would be more time consuming to correct
on the assembly line.

On the basis that the vehicle would be required to meet emis-
sion certification standards at the minimum idle speed, this speed
would then be essentially the low limit of the recommended idle
speed. When the total carburetor-engine-vehicle system tolerance
range is considered, it would result in being forced to select a
higher than desirable recommended idle speed. This would result
in owner complaints and increased service and warranty costs. ‘The
extent of this cost increase is not predictible since the degree
of the problem will not be known until considerable engineering
investigation is conducted.

A further problem relates to the impact this requirement
would have on the anti-dieseling solenoid controls now used which

|
function to close the throttle below curb idle when the ignition


-15-

Choke Bi-Metal Setting

This parameter is adjustable on the carburetors under study.
Preliminary designs to eliminate this adjustment are available and
could be tooled and implemented by the 1980 model year. We antici-
pate a piece cost increase of 25¢ over the current design bi-metal
assembly with a tooling cost of approximately $60,000. The costs
are estimates by the contractor. Accurate costs from the suppliers
would not be available until final designs are completed. The
change would have no significant impact on the manufacture of the
earburetor or vehicle. It would have no impact on emission certi-
fication.

It is an adjustment used in the field to correct driveability
complaints, however, its effectiveness is perhaps overrated. Used
indiscriminately, it can have an adverse effect on vehicle emis-

sions not commensurate to the gains achieved in driveability.


Section 1

Section 2

Section 3

Section 4

Section 5

Section 6
Section 7

Section 8

INDEX
Preliminary Meetings to Develop Scove of
Work and Other General Instructions
Scope of Work (Cbjective)

Contractor's Interpretation of the Regu-
lation

Rational and Approach

Listing of Industries with Whom the Con-
tractor Met During the Course of this
Study

Impact of the Froposed Regulation

Carburetor Deposits

Summary and Recommendations


-24-

become generally available before the concept of the non-service-

able carburetor can be introduced. Without such techniques avail-

able to all mechanics and technicians in the service industry, the

sale of replacement carburetors would increase needlessly, increas-

ing service costs.

Contractor's position on the seven parameters:

Idle mixture - We recognize that this may be a source of
misadjustment in the field and must be more effectively con-
trolled. A fixed idle setting without some means of adjust-
ment in service is not judged ‘practical at the state of the
art projected for 1980. Long term in use testing should be
conducted to gather more information. Should a fixed idle
setting or a fixed rich limit be ultimately adopted, it must
be preceeded by universally available diagnostic techniques

capable of identifying the cause of engine malfunctions.

Idle speed (minimum) - Although this is an external car-
buretor adjustment and could be included under the intent of
the proposed regulation we are concerned with the problems
inherent in its implementation including, to our knowledge,
the current lack of feasible designs. We are also not aware
of evidence that indicate emission reductions would be achieved

by such a requirement.

Choke bi-metal setting - This is an external adjustment

which could be eliminated if required. Servicing costs may


THE AUTHOR

Carl E. Burke recently retired from American Motors after 30
years of service. Prior to retirement he had held the position of
Director of Environmental and Energy Regulations immediately pre-
ceeded by the position of Chief Engineer of Power Plants and Emis-
sion Control. As Chief Engineer, he was responsible for power
plant design and development including the design and certifica-
tion of vehicle emission control systems. The author represented
the corporation on the Motor Vehicle Manufacturers Association in
various capacities and on the Coordinating Research Council. The
author is a member of the Society of Automotive Engineers. Prior
to working for American Motors, he was employed for a period of
10 years in engineering test and development of industrial, farm
equipment and truck engines. The author graduated from Michigan

State University with a BSME degree.


-11-

the calibration of these units change, a new mixture setting
may be required to maintain proper air/fuel ratio and idle
quality.

2. During the life of the vehicle, valve seating, piston
ring function, and other engine parameters deteriorate stress-
ing idle quality. The normal idle quality of a vehicle meet-
ing emission standards has very little margin, being set at
slightly less than best idle quality in the lean direction,
An older vehicle may require mixture adjustment to maintain
acceptable idle quality.

3. During the life of the vehicle, deposits form in the
carburetor originating from atmospheric contaminants, engine
blow-by, gasoline gums, and exhaust gas recirculation gases,
These deposits affect idle mixture, especially in the case of
deposits near the throttle plate and idle port and tend to
cause idle mixture to go richer. Deposits in other locations
in the carburetor have caused other areas of the calibration
to go rich or lean. Until such time as this problem is re-
solved, which will be covered in other areas of this report,
idle mixture adjustment is required to compensate for the de-
posit effects at idle.

4, The most practical and readily available method of
setting idle mixture in service to the requirements of ex-
haust emission control and the manufacturer's specifications
is the lean drop method. An adjustable idle mixture is re-

quired to use this method.


-14-

is shut off, Although other designs have been used to accomplish
this same function, they are more complex involving basic carbure-
tor design changes. The writer is refering to a design to cut off
idle fuel flow at engine ignition cut off. Costs are not avail-
able since a design on which to base a cost is not available on
_the two carburetors under study. We question that lead time is
adequate should this route be selected.

Many factors affect idle speed of vehicles in use such as
break-in, climatic conditions, and varying engine conditions. An
excessively high idle speed which may result from a minimum limit
device on the carburetor cannot be tolerated since, with automatic
transmissions, it stresses the brake system and can result in
safety hazards. There must be a method available to reduce idle
speed and it is the writer's opinion that the manufacturer would
be forced to accomplish this by other means should control be
limited at the carburetor. This would increase the cost of the

system.