Carburetor Specifications
1928-1930
FLOAT LEVEL
Stromberg Carburetors
Stromberg U-1 and U-2 carburetors were used on the 1930 models of Durant. It has been found in service that in localities where different specific gravity fuels are used that the fuel actually affects the float level adjustment. When carburetors are shipped from the Chicago factory, they are set for fuel (petrol) of specific gravity .7608 to .7368 or 54° to 60° Baume When higher test (lower specific gravity) 68° to 70° Baume fuel is used the float level rises and by bending the float arm the gasoline level is brought back to normal. A table of correct specific gravity for all Strumberg models together with an illustrative cut, Fig. 12A, will be found on page 70 in the Chrysler section.
Stromberg Model U-2.–The correct float level setting is 3/64″ measured from the lower surface or the gasket face of the float chamber cover to the top of the float at the center. To adjust the float level, remove the cover to which the needle valve and float assembly are attached. Hold the assembly in an inverted position and bend the float lever arm until the correct measurement is obtained.
Stromberg Model U-l.–The correct float level setting is 11/64″ measured from the lower surface or gasket face of the float chamber cover to the top of the float at the center. To adjust the float level, remove the cover to which the needle valve and float assembly are attached. Hold the assembly in an inverted position and bend the float lever arm until the correct setting is obtained.
Tillotson Carburetors
Two points should be considered when checking float level on Tillotson carburetors. One is the height of the gasoline level in the carburetor bowl and the other is the full movement of the float. In service conditions may be encountered where someone unfamiliar with the proper carburetor calibration has attempted to make a float level adjustment by bending the float lever arm. This practice generally will result in shortening the travel of the float thus shortening the travel of the float valve. If the travel of the float valve is shortened, it causes the valve to fall to open wide enough to admit sufficient gasoline to supply the motor at high speeds thus causing a condition of leanness as the result of a lack of fuel.
Tillotson 1″ Carburetors.–The float level adjustment for all 1″ Tillotson carburetors used on Durant automobiles is the same. To determine the correct float level, remove the carburetor bowl cover. The level of the gasoline in the bowl should be exactly 13/16″ below the machined top edge of the float chamber. Adjust by moving the bushing on the needle valve.
Tillotson 1 1/41” Carburetors.–The float level adjustment for all 1 1/4″ Tillotson carburetors used on Durant automobiles is the same. The level of the gasoline in the carburetor bowl should be 15/16″ below the machined top edge of the float chamber. Adjust by moving the bushing on the needle valve.
CARBURETOR SPECIFICATION DIAGNOSIS
Carburetor Specification Information.–Two makes of carburetors, Stromberg and Tillotson, have been used as standard equipment on Durant automobiles. The jet specification information for each make of carburetor is given in the following paragraphs under the heading of the carburetor. Instructions on how to use the specifications and determine the correct carburetor calibration is also given under the carburetor heading for each carburetor.
Jet Measurement.–All jet and nozzle measurements for both makes of carburetors used on Durant are given either in wire drill size or thousandths of an inch. Venturi tube measurements are given in fractions of an inch. A table containing wire drill sizes from No. 1 to No. 80 in terms of thousandths of an inch and metric drill sizes is given below.
Drill Sizes–The following table contains twist drill arid steel wire gauge sizes and areas together with nearest equivalent metric sizes.
STROMBERG CARBURETORS
The jet specification, information for all models of Durant equipped with Stromberg carburetors Model U were used; Models 6-14 and 6-17 came equipped with Stromberg U-2 while Model 407 equipped with U-1. The specification diagnosis information is the same for both models but the internal specifications are different.
The specification diagnosis information is given first followed by a table of carburetor specifications for each size of carburetor used. All Stromberg carburetor specifications are given either in wire drill sizes or thousandths of an inch. The main metering jet and economizer by-pass jet sizes are given in thousandths of an inch while all other specifications are wire drill sizes except Venturi tube measurements which are given in fractions of an inch. Under the heading of Jet Measurements above a table containing twist drill and steel wire gauge sizes and areas together with nearest equivalent to metric sizes will be found. For information as to how to read Stromberg Model numbers, see information on page 74, Chrysler section, under the heading How to Read Stromberg Model Numbers.
Specification Diagnosis
(Stromberg Model U)
Stromberg Models U-l, U-2.–The following information is given to enable the mechanic to properly diagnose a condition where jet sizes have been changed by drilling or soldering up holes or where jets have been replaced and adjustments changed. Occasionally. Carburetor specifications will be changed by drilling out jet openings. This should never be done under any consideration. Take for example, idling jets or the air bleeder. In many cases, these openings are made in the carburetor body and drilling out these openings will necessitate installing a new carburetor body in order to obtain the original jet size. When trouble is experienced with the carburetor, it should be remembered that there are seven places at which the internal adjustments may be changed to effect its operation. When attempting to determine these changes, the work should be done in order as given below.
Idling Discharge Jet (Stromberg U-I, U-2).-The idling discharge openings are made in the carburetor body and should not be drilled out under any consideration. Jobs with idling jets too small will rarely, if ever, be encountered but occasionally a job will be encountered where someone unfamiliar with the seriousness of tampering with the idling jets has drilled out the openings. In these cases, it will generally be found necessary to replace the carburetor body in order to restore the original correct opening sizes.
Diagnosis, Idle Jets too Large.–lf the idling jets are too large the motor will Roll and load regardless of how much air is admitted through the idle adjustment. Also, the motor will have a tendency to idle fast with throttle completely closed.
Main Metering Jet (Stromberg U-l, U-2).–The main metering jet or high speed adjustment (I) Fig. 6, controls the flow of gasoline for speeds will be found under the heading of Specification· above 20 miles per hour. This jet may be either of Diagnosis below. Two sizes of the Stromberg the fixed size or adjustable type.
Diagnosis, Metering Jet too Large.–To determine whether the metering jet is too large the car should be tried out on a hill steep enough that with wide open throttle a car speed not to exceed 10 miles per hour in high gear can be maintained. If the metering Jet is too large, a tendency to Roll and load will be noticed just as the as the load on the motor is lightened by the car passing over the brow of the hill with the throttle still fully open.
Generally, when the main metering jet is too large, the car owner will complain of poor gasoline mileage at all speeds with a tendency, in some cases for the motor to rub rich on a level road. It may also be found that when starting a cold motor the choke can be released immediately. In localities where a hill suitable for testing is not available, the trouble can generally be checked out on a level road test by accelerating the car with wide open throttle in second gear. If the metering jet is too large, the motor will probably have a tendency to stumble during the period of fast acceleration. If this is found to be the case, change the metering jet to a smaller size (approximately two sizes on first test) and test the car again with wide open throttle in second gear.
If reducing the metering jet size corrects the trouble, the car performance will be smooth through the full range of fast acceleration. However, if the cause of the range of fast acceleration. However, if the cause of the trouble is not due to a main metering jet that is too large, then reducing the size of the jet will probably cause the motor to sputter in the carburetor accompanied in most cases with a loss of power and speed.
Diagnosis, Metering Jet too Small–If the main metering jet is too small, the car will have a tendency to stall on a light grade when the motor is throttled fully open down to approximately 7 or 8 miles per hour and then accelerated gradually to about one fourth throttle. The symptoms produced by a metering jet of the wrong size may be confused with a by-pass or main discharge jet of the wrong specifications. If after changing the metering jet to a larger or smaller size the trouble still exists or is exaggerated, the by-pass jet should be checked.
By-Pass Jet (StrombergU-1, U-2)—The by-pass jets shown as the by-pass restriction (T) Fig 6 The purpose of this jet is to supply an
increased amount of gasoline to the main discharge jet at speeds above 40 to 45 miles per hour or any condition that requires a wide open throttle. Three conditions of trouble may be encountered in connection with the by pass jet. Namely, the by-pass jet may be too large; the by-pass or economizer valve may stick or not seat properly due to wear or warp or the by-pass jet may be too small.
Diagnosis By-pass Jet too Large.–lf the by-pass jet (T) Fig. 6 is too large, the car owner will probably complain of low gasoline mileage at car speeds above 40 miles per hour. To check for this condition, the car Should be tried out on a hill steep enough that with wide open throttle a car speed not to exceed 10 miles per hour in high gear can be maintained. If the by-pass is too large, a tendency to Roll and load will be noticed just as the load on the motor is lightened by the car passing over the brow of the hill with the throttle still fully open. If no hill is available that is steep enough for a test, the car can be tried out under level road conditions by first substituting a smaller by-pass jet and then trying the car out under level road conditions to see that it Does not have a tendency to load under wide-open throttle conditions. When reducing the size of the by-pass jet, following instructions are recommended. If the by-pass jet in the carburetor is over .040”, try five sizes smaller. However if the by-pass jet in tile carburetor is less than .040″, try two sizes smaller on first test.
Diagnosis, By-pass Valve Sticking–The by-pass valve may stick or not seat properly due to wear or warp. It this condition exists, the carburetor may be affected at moderate speeds (20 to 35 miles per hour) resulting in low gasoline mileage. This trouble may also make a correct carburetor adjustment difficult. To correct this condition, replace with new by-pass valve.
Diagnosis, By-pass Jet too Small–If by-pass jet is too small, the car owner may complain of lack of power at speeds and on heavy pulls accompanied in some instances by a condition of motor hesitation similar to cutting out of the ignition. To check, try the car out on a hill steep enough to require a full open throttle. Depending upon the individual characteristics of the car, a by-pass Jet that is too small may show up in lack of speed and power with an occasional sputtering or cutting out of the motor or a condition may exist where when the throttle is fully open the car will have a decided flat spot but as the throttle is partially closed, the motor will pick up. A tendency to poor acceleration will prevail under all conditions. If the trouble symptoms indicate a small by-pass jet try a jet one or two sizes larger.
Main Discharge Jet (Stromberg.U-1, U-2)—It is seldom in actual practice that a large main discharge jet (P) Fig. 6 will have any affect on carburetor performance other than to lower the gasoline mileage. This condition holds true, however, within certain limits. By that we mean that a main discharge jet may be so large that it will throw the carburetor out of balance. Care should be exercised not to confuse the symptoms caused by a large main discharge jet with those produced by a large by-pass jet. If the trouble is actually caused by a large main discharge jet, reducing the size of the by-pass jet may correct the loading on a pull but if the motor continues to load and Roll at high speeds, the trouble will probably be caused by a main discharge jet that is too large. Care should also be exercised not to confuse the trouble caused by a large main discharge jet with a Venturi that is too small. (See information below for small Venturi).
Diagnosis Main Discharge Jet too Small–If the main discharge jet (P) Fig. 6 is too small, the gasoline mileage may be good but the car will be slow on acceleration and lack speed and power especially on a hard pull (see paragraph above).
High Speed Air Bleeder (Stromberg U-l, l J-2). –The high-speed air bleed and main discharge jet have been calibrated at the factory to work in perfect balance; therefore any changes of the air bleed should be avoided. In the back of the book will be found more complete information explaining the purpose of the high-speed air bleeder (sec index in the front of the book).
Diagnosis, Air Bleeder too Large–If the air bleeder is too large, the trouble may be indicated by a sputtering of the motor on fast acceleration or a hesitation on slow acceleration. Sometimes at extreme high speeds a gentle popping in the muffler will be produced similar to the exhaust noise produced when coasting down a hill at a high rate of speed with the throttle closed and the ignition switch turned on. The car owner may complain of a tendency for the motor to hesitate on slow acceleration and in some cases the motor may die in traffic.
It should be remembered that on some Stromberg models the high-speed air bleeder is drilled in the body of the carburetor while on other models the air bleeder is a changeable part. If the carburetor giving the trouble has the air bleeder drilled in the body, turn to the pecification table, which contains the correct drill size specifications for the particular carburetor model in question. These carburetor specifications will be found in the table at the end of each specification diagnosis section for the particular carburetor model in question. After the correct air bleed wire drill size is known, see whether someone unfamiliar with the correct carburetor calibration procedure bas drilled out the air bleed opening. If the air bleed opening has been drilled out, it may be necessary in order to correct the trouble to replace the carburetor body. However, if the air bleeder is of the changeable type, a smaller air bleeder may be used. In most cases an air bleeder that is too large can be checked out on level road test by slowly accelerating the car to approximately 25 miles per hour with the spark half retarded. If the air bleed opening is too large from one to three flat spots will probably be experienced and in some cases accompanied by a popping back of the motor during the period of slow acceleration.
Diagnosis, High Speed Air Bleeder too Small–If the high speed air bleeder is too small, the car performance on level road test Will be similar to a condition of late ignition timing or retarded spark. The motor will be logy on acceleration and at road speeds· The car owner may complain of low gasoline mileage at all car speeds accompanied by a tendency in extreme cases for the motor to Roll and load at low speeds and on acceleration. On a level road test with wide-open throttle, the car will lack speed and power. In most cases the trouble can be checked out by the same test procedure used for a large metering jet. The car should be tried out on a hill steep enough that with wide open throttle a car speed not to exceed 10 miles per hour in high gear can be maintained. If the high-speed air bleeder is too small a tendency to Roll and load will be noticed just as the load on the motor is lightened by the car passing over the brow of the hill with the throttle still fully open. Care should be exercised not to confuse a condition caused by an air bleeder that is too small with a main metering jet or bi-pass that is too large.
If a hill suitable for test purposes is not available the trouble can generally be checked out by level road test in the following way. First replace the air bleeder with a larger size (not to exceed four sizes larger on the first test). It should be remembered, however, that on some Stromberg models the high-speed air bleeder is drilled in the body of the carburetor while on other models the air bleeder is a changeable part. If the carburetor giving the trouble has the air bleeder drilled in the body, do not tamper with it other than to see that the passageway is clean. However, if the air bleeder is of the changeable type someone unfamiliar with the correct carburetor calibration procedure may have reduced the size. Next take the car out on a level stretch of road and accelerate slowly up to approximately 30 miles per hour. If the air bleeder was too small, motor performance should be improved when a larger opening is used but if no change is noticed or if the trouble is exaggerated, check for a main metering jet or by-pass jet that is too large·
Accelerating Pump (Stromberg U-l, U-2)–The pump reducer (K) Fig 6 regulates the flow of gasoline from the accelerating pump and affects the operation of the carburetor during quick acceleration. On Model U carburetors with manual controlled by-pass or economizer valve make sure that the roller of the throttle accelerating pump lever is in contact with the pump lever arm when the throttle is in closed position.
Diagnosis Pump Discharge Jet too Large or too Small–If the pump discharge jet is too large the motor will stumble on quick acceleration. If the jet is too small, the motor will usually backfire on quick acceleration. The trouble may be corrected by either increasing or reducing the size of the discharge jet as indicated by the symptoms of the trouble.
Venturi Tubes (Stromberg U-l, U-2)–Two types of van turf tube design are used in Stromberg Model U carburetors. In one type the yen turf is cast in the carburetor throttle body and in the other type the Venturi is a separate unit that can be changed. In practice it is seldom that trouble from a Venturi tube of wrong size is experienced. On the interchangeable type, the Venturi is locked into place by a setscrew that may work loose. Before testing for wrong Venturi size, see that the setscrew is tight.
Diagnosis– Venturi too Large—H the Venturi size is too large, motor acceleration may be smooth but slow similar to a condition that would be caused by a small main discharge jet, As the car gains momentum on acceleration, the motor performance will improve until at high speeds the carburetor operation may be fairly satisfactory with good gasoline mileage.
Diagnosis, Venturi too Small–If the Venturi is too small the motor will have good power on acceleration at wide open throttle under 20 miles per hour but as. The car picks up momentum and the load is lightened with throttle still wide open, the motor will have a tendency to Roll and load. On a level stretch of road with throttle wide open, the car will lack speed and gasoline mileage will be poor.
TILLOTSON CARBURETORS
Important Information–The jet specification information for all models of Durant equipped with Tillotson carburetors is arranged by carburetor model rather than by car model· To find the jet specification information for any particular model of Durant determine the model of carburetor by either referring to the table of motor specifications under Carburetor Adjustment or by examining the name plate of the carburetor. All Tillotson. Specifications except Venturi sizes are given in wire drill sizes in the table of Drill Specifications. Venturi sizes are given in fractions of an inch. In every case where trouble is experienced in obtaining a correct carburetor adjustment and all other units such as ignition, spark plugs, etc., have been accurately checked, the carburetor should be first removed and thoroughly cleaned.
Tillotson Model R-4A and R-6A Carburetors. In service mechanics who do not understand these carburetors attempt to improve the performance by drilling out the nozzle holes. This should never be done under any consideration. The adjustment needle is for the purpose of varying the gasoline mixture and takes care of the carburetor through its complete range of adjustment.
To enable the mechanic to determine whether or not the internal carburetor specifications have been changed, complete wire drill specifications for all Model R carburetors used on Durant are given in the following tables. When checking drill specifications, extreme care should be exercised not to damage the openings in any way.
| Drill Specifications (Tillotson Model R4A) | |
| Number DRILL | Description of part off holes size |
| Venturi Upper 13/16”. ………………………..…….. | |
| Venturi Lower 5/16” ……………………………..….. | |
| Main Nozzle (Upper Holes) …………………..…..2 | No. 42 |
| Main Nozzle (Middle Holes) ………………………2 | No. 48 |
| Main Nozzle (Lower Holes) ……………………….1 | No. 65 |
| By-Pass Upper Supply Hole (in body casting). ……..1 | No. 70 |
| By-Pass Lower Supply Hole (in body casting) ………1 | No. 56 |
| By-Pass Air Adjusting Hole ……………….…….1 | 3/32″ |
| By-Pass Air Bleed Hole ……………………..……1 | No. 60 |
| By-Pass Fuel Restriction Hole ……………….…..1 | No.74 |
| Fuel Adjusting Hole ………………………….…….1 | No. 55 |
| Inner Well Air Bleed Hole …………………..……1 | No. 36 |
| Outer Well Air Bleed Hole …………………..……1 | 5/32″ |
| Drill Specifications (Tillotson R6A) | |
| Number DRILL | Description of part off holes size |
| Venturi Upper 27/32′ . ………………………..…….. | |
| Venturi Lower 5/16″ ……………………………..….. | |
| Main Nozzle (Upper Holes) ……………….….2 | No. 52 |
| Main Nozzle (Middle Holes) ……………….…2 | No. 52 |
| Main Nozzle (Lower Holes) ………………..…2 | No. 65 |
| By-Pass Upper Supply Hole (in body casting)……………………….…1 | No. 70 |
| By-Pass Lower Supply Hole (in body casting)……………………….…1 | No. 58 |
| By-Pass Air Adjusting Hole …………………..….1 | 3/32” |
| By-Pass Air Bleed Hole ……………………..……1 | No. 60 |
| By-Pass Fuel Restriction Hole ……………….…..1 | No. 74 |
| Fuel Adjusting Hole ………………………….…….1 | No. 60 |
| Inner Well Air Bleed Hole …………………..……1 | No. 36 |
| Outer Well Air Bleed Hole …………………..……1 | No. 50 |
Tillotson Model SP-13A and SP-13B Carburetors–If trouble is experienced in obtaining a correct Carburetor adjustment, the carburetor should be removed from the car and all jets and passageways thoroughly cleaned, to see that no dirt has lodged in the openings. If this does not correct the trouble, it may be that someone has tampered with the carburetor. In service, mechanics who do not understand these carburetors attempt to improve the performance by drilling the nozzle holes. This should never be done under any consideration. The adjusting needle is for the purpose of varying the gasoline mixture and takes care of the carburetor through its complete range of adjustment.
In order to enable the mechanic to determine whether or not the internal carburetor specifications have been changed, complete wire drill specifications for the SP models of Tillotson used on Durant arc given in the following tables. Extreme care should be exercised when checking drill and nozzle openings not to damage the openings by carelessly inserting the drill.
| Drill Specifications (Tillotson SP-13A) | |
| Number DRILL | Description of part off holes size |
| Venturi Upper 29/32″………………………..…….. | |
| Venturi Lower 5/16″ ……………………………..….. | |
| Main Nozzle (Upper Holes) ……………….….2 | No. 60 |
| Main Nozzle (Middle Holes) ……………….…2 | No. 65 |
| Main Nozzle (Lower Holes) ………………..…2 | No. 60 |
| By-Pass Upper Supply Hole (in body casting)……………………….…1 | No. 70 |
| By-Pass Lower Supply Hole (in body casting)……………………….…1 | No. 58 |
| By-Pass Air Adjusting Hole …………………..….1 | 3/32” |
| By-Pass Air Bleed Hole ……………………..……1 | No. 60 |
| By-Pass Fuel Restriction Hole ……………….…..1 | No. 74 |
| Fuel Adjusting Hole ………………………….…….1 | No.56 |
| Inner Well Air Bleed Hole …………………..……1 | No. 36 |
| Outer Well Air Bleed Hole …………………..……1 | No. 52 |
| Drill Specifications (Tillotson SP-13B) | |
| Number DRILL | Description of part off holes size |
| Venturi Upper 29/32″………………………..…….. | |
| Venturi Lower 5/16″ ……………………………..….. | |
| Main Nozzle (Upper Holes) ……………….….2 | No. 60 |
| Main Nozzle (Middle Holes) ……………….…2 | No. 65 |
| Main Nozzle (Lower Holes) ………………..…2 | No. 60 |
| By-Pass Upper Supply Hole (in body casting)……………………….…1 | No. 70 |
| By-Pass Lower Supply Hole (in body casting)……………………….…1 | No. 58 |
| By-Pass Air Adjusting Hole …………………..….1 | 3/32” |
| By-Pass Air Bleed Hole ……………………..……1 | No. 60 |
| By-Pass Fuel Restriction Hole ……………….…..1 | No. 70 |
| Fuel Adjusting Hole ………………………….…….1 | No.56 |
| Inner Well Air Bleed Hole …………………..……1 | No. 36 |
| Outer Well Air Bleed Hole …………………..……1 | No. 52 |
Tillotson Model V-1A Carburetor—Tillotson Model V carburetors are similar to the SP type with the exception of the high speed adjustment. Mechanics who do not understand Tillotson carburetors attempt to improve the performance by drilling out nozzle holes. This should never be done under any consideration. The adjusting needle is for the purpose of varying the gasoline mixture and takes care of the carburetor through with the exception of the high speed adjustment. To enable the mechanic to determine whether or not the internal carburetor specifications have been changed, complete wire drill specifications for Tillotson Model V carburetors used on Durant are given in the following tables.
| Drill Specifications (Tillotson V-1A) | |
| Number DRILL | Description of part off holes size |
| Venturi Upper 1 5/32″………………………..…….. | |
| Venturi Lower 7/16″ ……………………………..….. | |
| Main Nozzle (Upper Holes) ……………….….2 | No.60 |
| Main Nozzle (Middle Holes) ……………….…2 | No.60 |
| Main Nozzle (Lower Holes) ………………..…2 | No.58 |
| By-Pass Upper Supply Hole (in body casting)……………………….…1 | No.70 |
| By-Pass Lower Supply Hole (in body casting)……………………….…2 | No.58 |
| By-Pass Air Adjusting Hole …………………..…. | No.60 |
| By-Pass Air Bleed Hole ……………………..…… | No.60 |
| By-Pass Fuel Restriction Hole ……………….….. | No.70 |
| Fuel Adjusting Hole ………………………….……. | No.52 |
| Inner Well Air Bleed Hole …………………..…… | No.36 |
| External Well Air Bleed Hole ………………….. | No.35 |
| Pump Delivery Nozzle ………………………….. | No.55 |
| Internal Air Bleed Hole …………………………. | No.50 |
Carburetor Adjustment
MOTOR SPECIFICATIONS
The following table lists the model and year of car, engine specifications, make, model and size of carburetor.
| DURANT STROMBERG | |||||
| 1930 | 6-14 | Cont. 22A | 6 | 3 ¼”X4” | U-2 |
| 1930 | 6-17 | Cont. 15U | 6 | 3 ¼”X4” | U-2 |
| 1930 | 407 | Cont. W-8 | 6 | 3 7/8”X4 1/4” | U-1 |
| TILLOTSON | |||||
| 1928 | M4 | Cont. | 4 | 3 3/8”X4¼” | R 6A-1 |
| 1928 | 55 | Cont. 14L | 6 | 2 ¾”X4 ¾” | R 4A-1 |
| 1928 | 65 | Cont. 15L | 6 | 2 7/8”X4¾” | SP-13A |
| SP-I3B, R4A-I | |||||
| 1928 | 75 | Cont. 15U | 6 | 3 3/8”X4 5/8” | V-1A-1¼” |
| 1929 | 40 | Cont. W-5 | 4 | 3 3/8”X4¼” | R-6A-1“ |
| 1929 | 60 | Cont. 14L | 6 | 2 7/8:X4¾” | SP-13B-1” |
| 1929 | 66 | Cont. 14L | 6 | 2 7/8X4¾” | R-4A-1” |
| 1929 | 70 | Cont. | 6 | 3 3/8”X4 5/8” | R-4A-1 ¼” |
ADJUSTMENT PRECAUTIONS
Sleeve Economizer.–It is important on all Tillotson type carburetors equipped with sleeve type economizer to see that the economizer is properly adjusted. If the economizer valve is open at low speeds, motor performance will be affected in that it will be difficult to obtain a smooth idle or low speed adjustment. As shown in Fig. 7, the economizer should be adjusted with a 1/64″ to a 1/32″ overlap in the closed position when the carburetor throttle valve is completely closed. This adjustment can be obtained by loosening the set screw (A) and moving the control arm on the end of the economizer shaft. If difficulty is experienced in obtaining an adjustment or if car performance does not seem to be correct after a proper adjustment of the economizer has been made, check to see that the economizer sleeve is not worn excessively. Also check to see that the throttle shaft is not badly worn. If the throttle shaft or economizer sleeve is worn to the point of where car performance is affected, replace with new part.
Manifold Effect on Carburetor Adjustment. It is important when making a carburetor adjustment that from I0 to 15 seconds time be allowed for each movement of the adjusting screw at the bottom of the carburetor. This is necessary to Know time for fuel that has accumulated in the manifold to pass into tile motor. Take for example all adjustment from a rich to a lean mixture. The tendency is for the fuel to pile up on the walls and in the corners of the manifold so that unless sufficient time is allowed for this fuel accumulation to pass into the motor, an accurate adjustment cannot be obtained. Insufficient time allowance is generally indicated by the motor performance gradually improving and then the motor suddenly dying during the adjustment operation.
Adjustment for Gasoline Mileage.–The best adjustment for gasoline economy is obtained by leaning the mixture down until the motor runs rough and then richening it up just to the point of where the motor runs smooth. This is especially true of the idle and high-speed adjustment and should be done with care for best results. When adjusting the carburetor from a lean to a richer condition, it will be found that due to the flexibility of adjustment, there is a wide range between the point where the motor smoothes out from a lean mixture to a point of where the adjustment is too rich. Richening of the mixture beyond the point of smooth motor operation adds nothing to the performance of the car and lowers the gasoline mileage.
TILLOTSON MODEL R
In order to obtain an accurate and correct adjustment of a Tillotson carburetor, all other units on the engine such as ignition points, spark plug points, motor compression, etc., should be in good condition. See that all special instructions given in the section following the Motor Tune-Up have been checked. Also refer to Adjustment Precautions above for special information regarding carburetor adjustment.
The Tillotson Model R carburetor used on Durant automobiles is of the non air valve type having two adjustments, namely, the by-pass adjustment for idle and low speeds and the needle adjusting screw for medium and high speeds, see Fig. 8. The idle nozzle gets its fuel from the main nozzle; therefore, the main nozzle should be adjusted first.
High Speed Adjustment.–To adjust the carburetor after it has been completely overhauled and replaced on car, proceed as follows: Close the main adjusting screw (A) Fig. 8 to its seat (do not force against seat) then open two or three turns to the left or down. Close the by-pass or idle adjustment screw (B) to its seat. Then open to the left or out one turn. Start the motor and set the throttle on the steering column about one third open or to a position where the motor will be running at approximately 30 miles per hour car speed and keep the throttle in this position until the adjustment is completed.
After the motor is thoroughly warmed up retard the spark lever fully and with the motor running at the same speed, turn the high speed adjustment (A) slowly to the right or up until the engine slows down for want of fuel. At this point, turn very slowly in the reverse direction (usually from one fourth to three eighths of a turn) to that point, where motor runs at maximum speed. Do not open the high-speed adjustment beyond the point of where the motor smoothes out and runs at maximum speed since the most economical motor performance will be obtained with the needle Valve in this position.
Low Speed Adjustment.–Close the throttle and make sure that the throttle stop screw does not allow the throttle to become fully closed. Then to get the proper idling mixture, turn the adjustment thumbscrew (B) Fig. 8 to the left or anti-clockwise admitting more air and making the mixture leaner. Continue to turn until motor sputters or misses. At this point, turn slowly in the reverse direction to that position where the engine again fires evenly. After the idling mixture is correct, which should be approximately one full turn from a fully Seated position, adjust the throttle stop screw to the proper idling speed of the motor.
TILLOTSON MODEL SP
Important–Before changing the carburetor adjustment, make sure that the trouble does not lie elsewhere. Examine the spark plugs and breaker points to see that they are correctly set and that the choke is in full open Position; also refer to the tune-up precautions immediately following the Tune-Up Operations and check all items that would affect the carburetor performance. Read the adjustment precautions given above.
High Speed Adjustment–Close the main adjusting needle (D) Fig. 9 by turning to the right or up until the needle is seated (never force tightly against its seat). Then open by turning to the left or down two complete turns. Close the by-pass or idle adjustment (E) until it is seated by turning to the right or in, then open by turning to the left or Out one half turn. Thus adjusted, the engine should start and operate.
With the throttle partly open to an engine speed of approximately 25 miles per hour, allow the motor to warm up to normal driving temperature. After the motor has warmed up, retard the spark control lever fully and gradually turn the main adjusting needle to the right or up to a point where the engine slows down for want of fuel. When this point is reached, stop and gradually turn in the reverse direction until that position is found where the engine runs smoothly. This adjustment should be carefully made for gasoline economy cannot be obtained if the needle is allowed to pass over the point of sufficient fuel delivery to give good power and run smoothly. Provision for maximum power is automatically supplied so that care should be exercised in adjusting the main adjustment needle (D) to provide for economical road performance. After the high-speed adjustment is complete, next adjust the idling screw (E).
Idle Adjustment.–Turning the idle adjusting screw (E) Fig. 9 to the right (clockwise) gives a richer mixture; turning it to the left (anti-clockwise) gives a leaner mixture. This adjustment is sensitive and should be made with care. Close the throttle fully and with the spark still retarded, set the throttle lever stop screw to run the engine at slightly faster speed than is desired for normal idling conditions. Turn the low speed adjusting needle (E) gradually to the left or out until a noticeable flutter or missing occurs. At this point turn the screw in the reverse direction to that position where the engine again fires evenly. Leave the adjustment at this position, that is, delivering just as thin a mixture as will properly idle the engine. Next, carefully adjust the throttle lever stop screw to operate the engine at the desired idling speed.
Accelerating Pump.–Sudden enrichment of the mixture is necessary to quick engine acceleration, and additional power for maximum speed. The carburetor is equipped with an accelerating pump for this purpose when the throttle is suddenly opened; the piston of the accelerating pump is raised lifting fuel into the upper chamber. (Sec Fig. 10). This small amount of fuel flows through the metering nozzle leading directly into the Venturi tube at the point where the rush of air is at its height, and the mixture is instantly enriched to proportion for maximum power. While driving at normal speed with the throttle partly open, the mixture is regulated for maximum economy. When the throttle is opened wide, the carburetor delivers the proper mixture for maximum power.
Dash Control or Auxiliary Lift Needle–In starting a cold engine the carburetor dash control should be pulled out all the way and as soon as the engine starts the control should be moved slightly inward. This automatically supplies a rich mixture to the engine, thus enabling it to start easily. The dash control should be pushed in all the way just as soon as the engine is warmed sufficiently to run without spitting back into the carburetor. Avoid excessive use of the dash control since this is likely to cause crankcase dilution. Do not use dash control to start when the engine is warm. To adjust the dash control to the carburetor, see that the choke lever is as far back as it will go with the control
fully seated.
If it should become necessary to reset the lift or metering pin, proceed as follows: With the throttle closed and the choke fully opened, there should be a minimum of .030″ to .040” play between the adjustable nut (G) Fig. 10 and the fork (H) of the cross lever. There should always be sufficient play between the lever coupling, the choke cam and the needle lift lever to insure a seating of the needle.
As shown in Fig. I0 the metering or economizer needle (I) also provides a richer mixture for power purposes at high speeds with the throttle opened. Thus, it is important that the economizer needle adjustment be accurately made as described above.
TILLOTSON MODEL V
The Model V Tillotson is a plain tube expanding type of carburetor having fixed air passages while the fuel is automatically controlled in proportion. The carburetor is designed to give maximum power and economy with ordinary fuel. Before changing the carburetor adjustment, make sure that the trouble does not lie elsewhere. Check the spark plugs and breaker points to see that they are correctly set and that the choke is in the full open position.
High Speed Adjustment–If the carburetor has been dismantled for any purpose, adjust as follows: Close the high speed adjusting needle (A) Fig. 11 by turning to the right or down until the needle is seated (never force tightly against its seat). Then open by turning to the left or up three complete turns. Next close the by-pass or idling adjustment (B) until it is seated by turning to the right or in, then open by turning to the left or out three-quarters to one full turn. Thus adjusted, the engine should start and operate.
Retard the spark control lever fully. With the engine running approximately 25 miles per hour car speed, gradually turn the main adjusting needle (A) to the right or up to a point where the engine slows down for want of fuel. When this point is reached, stop and gradually turn in the reverse direction until that position is found where the engine runs free. This adjustment should be carefully made for gasoline economy cannot be obtained if the needle is allowed to pass over the point of sufficient fuel delivery to give good power and smooth running. Provision for maximum power is automatically supplied through the accelerating pump and the needle lift, so in adjusting, set the main adjustment to provide for economical road performance.
Cross-section view of Tillotson Model V carburetor showing a cross section view of a high speed Adjustment (A). Model V Carburetors are different from the SP type in that the high-speed adjustment it mounted behind the bowl at shown while on the SP type the high-speed adjustment is located at the bottom of the carburetor.
View of Tillotson Model V Carburetor used on Durant automobiles showing a sectional view of the high-speed adjustment and auxiliary starting nettle. The lilt of the auxiliary needle can be regulated by the nut (D).
Idle Adjustment–Close the throttle and with the spark control lever retarded, set the throttle lever stop screw to run the engine faster than is desired for normal idling speed. Next turn the idle adjustment (B) gradually to the left or out thinning the mixture until a noticeable flutter or missing occurs. At this point, turn the screw in the reverse direction only to that position where the engine again runs smoothly. Leave the adjustment at this position delivering just as thin a mixture as will properly idle the engine and carefully adjust the throttle lever stop screw to operate the engine at the desired idling speed. In operation, the carburetor is fully automatic except that at partial choke position as controlled through the manual choke control on the dash, fuel metering is governed by the usual high and low adjustment needles.
Lift or Metering Needle Setting.–The metering or economizer needle is affected by the dash control when starting and by the throttle lever at high speeds. In starting a cold engine, the carburetor dash control should be pulled out all the way and as soon as the engine starts, the control should be moved slightly inward. This automatically supplies a rich mixture to the engine, thus enabling it to start easily. The dash control should be pushed in all the way just as soon as the engine is warmed sufficiently to run without spitting back into the carburetor. Avoid excessive use of the dash control, as this is likely to cause crankcase dilution. Do not use dash control to start when the engine is warm. If it should become necessary to adjust the dash control to the carburetor see that the choke lever is as far back as it will go with the
controls fully seated.
If it should become necessary to reset the lift needle, proceed as follows: With the throttle closed and the choke fully opened, there should be a minimum of .030″ to .040″ play between the adjustable nut (C) Fig. 12 on the needle and the fork (D) on the cross lever. There should always be sufficient play between the levers coupling the choke cam and the needle cam lift lever to insure the seating of this needle.
Information Donated by Carol Rush