Venturi Operation Operation of a Simple Venturi ‘The Mikuni slide type carburetors described inthis manual are also known as “variable venturi” type carburetors. A ventu is restriction ‘within the carburetor designed to speed up the air flowing through the cath tis atthe point of the smallest cross section thatthe incoming air flow will have the greatest velocity. As airflow speeds up to pass through the venturi, loses pressure. tis at his point thatthe pressure within the carb throat wil be at its lowest; this is called “depression” At this point of maximum depression, the fuel wil be introduced tothe air stream. In order to transfer fuel from the fuel chamber into the Carburetor venturi, a small tube is placed int the ventur which connects the fue load in the chamber tothe venturi. The fuel chamber is open to ‘atmospheric pressure (15 psi approx) and the pick up tube is exposed to the depression within the venturi. The difference in pressure will attempt to equalize through the pick up tue, pushing ful from the fuel ‘chamber into the venturi. The fuel is mixed with the incoming ai and delivered tothe engine downstream. This is the basic principle by which all carburetors operate itis important to remember that itis the pressure difference ‘between the fuel chamber and the venturi which pushes the ful into the intake air stream. The presence of engine vacuum alone is nat enough to ‘ra fue! into the intake port, Without the atmospheric pressure in the fue chamber, the ful could not be delivered into the intake por. ‘The above mode! wl serve a single speed engine very well th the venturi becoming the throtle. The engine will run at one speed only, depending upon the size of the venturi. Because motorcycles are ‘operated at various engine speeds, there needs to be a way to control the speed ofthe engine. In order to throtle down this wide open carburetor design, Mikuni has inserted a slide which crosses the carburetor throat to contol air flow tothe engine, imiting engine speed according to slide lit. This side lit varies the cross section ofthe carburetor bore atthe venturi point This fs how slide carburetors become known as "variable venturi’ These variable venturi type carburetors are very good at maintaining high ai speeds within the carburetor throat and generally offer better Coverall performance than most other carburetor designs, From this simple fuel delivery circuit, carburetor designers wil add ‘and divide this circuitry in order to tailor the mixture avaiable to the engine, enabling ito un accurately ata wide varity of speeds and lads. Be od [eed fir @Fuel Operation of a Variable Venturi Al Mikuni motorcycle carburetors described in this manual are of the variable venturi type. With ths type of carburetor, the maximum depression zone is beneath the throttle valve (side) which is raised and lowered by the throttle cable, controling the speed of the engine ‘As shown in the drawing, the botiom of the slide features a tapered needle which its into the fuel pick up tube (nescle jet to meter the fuel delivery of the tube from about a 1/4 throttle to 3/4 throttle, From 3/4 to ful throttle, the needle wil be too narrow to affect the ful flow of the tube. From this point on, th fuel flow ofthe tube is metered bythe main jet which i postioned atthe bottom of the tube ‘The above description is a simple model of the main circuit ‘common to most Mikuni slide type carburetors, The following chapter Contains a more complete description of Mikuni motoroyle carburetor design and fuel delivry circuits ‘Maximum Depression Zone Bae Atmospheric Pressure (Tops!) ick up tube OAir @ Fuel fie fe Jet) <— fel Chamber JGeneral Mikuni © Slide Carb Circuitry This manual is intended as @ guide for users of Mikual carburetors who want to learn the basic methods of tuning and adjusting to obtain top performance and fuel economy. The arous that appear in the drawings inthis text show direction in which air, fuel, and a-uel mure flows. Information herewith obtained from Mikuni engineering data and manuals. 1. CARBURETOR FUNCTION ‘The function ofa carburetor is to deliver a combustible air-fuel ‘mixture tothe engine. However, inorder to be effective, t must frst break ‘the fuel nto tiny particles (in the form of vapor) an then mix the fuel with arin a proper rato sot can burn without leaving excess fuel or ar 2. AIR-FUEL MIXTURE (Fig.1) ‘The mixture ofthe air-fuel ratio is generally expressed by its relative weight proportion. For example, the amount of air required for complete combustion of 1 gram of fuel under normal conditions is ee Airtel mire Maxim power mature ratio 400 “Tote wave opening) 1Sgams ot Air > Ratio ‘amet Fuel = Mixture > Varying mixture ratios ae require forthe engine depending on ‘operating cantons. Although the required mixture ratio varies more or less with the type of engine is cooling efficiency, ec, the mixture ratio shown in fg. 1 is required for ordinary engines. Inthe high speed range the ratio of about 12 to 13 grams of at for 1 gram of fuel produces the ‘maximum output. However, in te case of an engine with low cooling efficiency, a somewhat richer mixture (10 to 12 grams of air against 1 gram of fue) may be require to prevent seizure of the engine, 3. FUNCTIONS AND CONSTRUCTION MIKUNI SLIDE TYPE CARBURETORS Motorcycle engines are operated under a wide range of ‘conditions, from ing with the throte valve (Fig.2(1) remaining almost closed, to the full oad (the maximum output) with the throttle valve ful ‘opened. In order to maet the requirements forthe proper micure ratio under these varying conditions, a low-speed fuel system (the pilot system) and a main fuel system (the main system) are provided in ‘Mikuni Side-type carburetors, except Mikuni TMS, eT Ta raed A. - The Pilot System Low-speed tuel system (Fig.2 and Fig.3) Since the engine is operated with the throttle valve almost closed at idling or in the low speed range, the velocity of air flowing through the needle jt (2) is slow. Consequently, a vacuum strong enough to draw fuel from the needle jet in main fuel system is not created. The fuel supply during this low speed operation is controled bby means of the pilot outlet (3) and the bypass (4) that are situated ‘nearest tothe engine. At idle, when the that valve is slightly opened, fuel metered by the pitt jt (5) is mixed with air acjusted in a proper ‘amount by the air sorew (6) and is broken into fine vapor particles cr ‘The minture is agsin mixed with ar coming from the bypass and is raw ito the plot otto mix wih i owing through the man bore (7) The fuel mod wit air at this stage then goes to into the engine, When the thro valve is opened sighly ding low speed operation, the plot outlet alone cannot supply the required fuel and the shortage has to be made up wth fuel injected from the from the bypass. The adjustment of the mixture ratio during this ‘stag is made by the pot et and the ar scrow, as in the case ofa two-hole type fuel system (Fig.3). While at low speed operation, if full throttle is inated. similar shortage of ‘uel agin has tobe injected from the bypass until enough (vacuum) can be created to raw fuel from the main fuel system, Theres 30 a one-holetype aw speed fuel system mainly usec for carburetors having a small main bore. The process of producing the air fue! mixture and of adjusting the mitre ratio are the same asin a two-hole ‘ype low speed system. TreeGeneral Mikuni Slide Carb Circuitry B. -Main Fuel System On Mikuni VMtype carburetors, the pilot system and the main system are of independent construction. The fel flown these two systems is shown in Fig. Ther ae two types of main ua system, one a primary ‘ype used widely or 2-cyle engines and the other i abled type which is normaly used for 4-oyle engines aswell as for rotary valve 2cyce engines, Sudco uses primary type needle jets in most 4-cycle VM applications, It is important to note (Fi.5) that the main system ‘minture delivery is in addition to the mixture delivered by the pilot system, Therefore, adjustments to the pilot system should be made first, as they will affect the adjustment of the main system to a diminishing extent as the throttle is opened from 1/4 to full throttle. ie Primary Type (Fig.6) When the throttle valve is opened about 1/4 or more, the velocity of air tlowing through the needle jt (10) increases and also the vacuum inreases to the point where fuel can be sucked in. When the opening of throttle vale (1) is between a quarter and three quarters, fuel passes through the main jet (9) and, after being metered in the clearance between the needle jt (10) and the needle (11), tis mixed with ai thats metered by the ai jet (12) and atomization o the fue is accelerated The mixture is then injected, after mixing with air flowing through the main bore (7), to the engine inthe optimum air-fuel ratio, During this process of operation, the cutaway of the throttle valve serves to control the vacuum on the needle jet, thereby regulating the amount of fuel that is injected to the engine. When the throttle valve is ‘opened more than three quarters high speed operation, fuel {is metered chiefly by the main et (9). ma Bleed Type (Fig.7) ‘The construction ofthe bleed-4ype (10) main fuel sytem i the same as that of the primary type, exoept forthe bleed oles that are provided in the needle as mea In the case of the primary type, air which comes from the main ar jot Is mixed with the raw fuel after it has been metered by needle jet and needle. This atomization takes place behind the nozzle screen or shroud above the Needle jet outiet. The bleed type on the other hand is designed to bleed the air coming from the main air jet into the body section of the needle jet where itis emulsified with the fuel coming up from the bottom. The needle jet and needle then meter a blend of aifue, resulting in a finer atomization and generally leaner mixture than the same size primary type needle jet. C. - Float System (Fig.8) ‘The float sytem serves to maintain a constant evel of fel in the bow Fuel flows through the needle vave (14) and enters the fat chamber (15). AS the fuel enters the float chamber, the lat (16) ‘moves upward to its pre-determined level because of Buoyancy. When the fuel reaches the pre-determined lve, the needle vale begins close de tothe lever action ofthe fot arm rising asthe float tains buoyancy, thus shuting off the suppy of fue The fuel level inthe bowl controls the amount of fuel wich is metered to make the optimum fuel mixture. For example, too high a level allows more fuel than necessary to leave the needle jet, enriching the mmidure, Too low @ level results in a leaner mixture, as not enough fuel leaves the needle jet. Therefore, the pre-determined fuel level should not be changed attra Gre fD. - Starter System (Fig.9) Rater than a choke, the envichener type starter system is employed for Mikuni carburetors ‘The enrichener slater type, fuel and. air, tor starting the engine are metered by entirely independent ts. Te ful metered by the starter jt (17) Is mixed with air and is broken int tiny particles in the emulsion tube (18). The mixture ‘nen lows into th plunge area (19), mixes again with coming from the ‘ear itake port for starting ais dered to the engin in the optimum aiefuel rato through the fuel discharge passage (21). The enichenr is ‘opened and closed by means ofthe starter plunger (22). Since the fevichener is contucte so as outize te vecium of he inet passape (20) tis irmportant thatthe hot valve is Cosed when starting the engine. 4, TUNE UP & CARBURETOR SELECTION Turing up normaly means a process of accurate and cael austen to obain maximum engne performance. Athough, it means in a broad sense, an economical improvement in uel consumption, Improvement of power ‘output ofthe engine depends onthe amount of ar draum into te ender per unite. A practice generally flowed for engine tune-up incades 1) Toimprove suction efficiency and exhaust efficiency ‘by remodeling the intake and exhaust system 2) Toimprove combustion efciency by raising the compression ratio. 3) Toincrease the numberof revolutions by adjusting the ignition timing ne Eee Primary Pe Syste Cea J Too large a main bore ean bore T elation pr mine om) A. - Carburetor Main Bore Size Selection (Oe ofthe prerequistes for improving the output isto use a carburetor wth as large a main bore as possible. However, alrge main bore alone does not necessarily improve the cudput. AS shown in Fig, re tat large ‘ain bore improves the power utputin the high speed range. Howeves, nthe ‘how sped range, the output may drop. The main bor size eecton should be ‘etermined by various factors such as (1) wheter the vehicle intended for racing, (2) the design of the engine (3) riding technique of he de, (4) the ‘der preference, ec. In ation, the maximum outpu, the maximum torque, andthe minimum numberof realstons for stable engine operation must aso be taken into account Fig.10 shows the values which we have obtained throughout experince over the yeas. ‘Since the engine comes ina wide varity of pes, the values given in Fig. 10 should be taken onl as reference values. 5. CARBURETOR SETTING ‘Once the main bore size of the carburetor is determined, a test (normally refered to as setting or matching) to select the proper jet ‘or setting part should be made. The size of the jt is determined by measuring the output in a bench or in a chassis dyno test. For racing, itis best to determine the proper size of the jet on the racing course The following points must be taken into account: 1) The altitude (atmospheric pressure), temperature and humidity ofthe racing course. 2) The operation of the engine based on the topography ofthe racing course. 3) Generally, carburetor tuning is done in four stages: ide, low speed, mid-range, and high ‘speed in that order. With the Mikuni, each ‘tage is controlled by a separate component ‘simplifying the tuning pracess. ‘The engine cylinders need to take sufficient air ‘and fuel mixed in proper amounts. The function of a carburetor isto prepare and supply a mixture of fuel vapor and air to the engine cylinders in the proper ‘aio fr efficient combustion.General Mikuni Slide Carb Circuitry A. - Pilot Jet and the Low Speed Fuel System (Fig. 15 & 16) (Air Screw type carburetors only) {nthe low speed fuel system of the carburetor, the pilot outlet and the bypass have holes winose size i in relation to the main bore of the carburetor. Hence, the adjustment and selection ofthe pilot et andthe air screw is important. Tur the throte a lite t no-load operation and 22 ff the engine revolution increases smoothly. Ifthe pilot et is too small, inrease inthe engine speed will be slow and irregular. Too big a pilot et, on the other hand, would give rise to heavy exhaust smoke as Well 2s'a dull exhaust nose. i you cannot maintain the speed in the ‘ange of 12-25 mph withthe throttle held,the pilots too smal, ‘Solection and setting ofthe air screw should be made in the following manner. First, warm up the engine adequately and set the ile ‘ore sO thatthe engine revolution at idling wil be about 10-20% higher than the number of evolutions you are aiming a. Then, tum the ar screw left and right (between 1/4 and 1/2 turn) and select the position where the engine revolution reaches the maximum. Adjust the idle screw to bring ‘down the engine revolution to your target speed for idling. After this adjustment of the idle screw is made, select once more the position ‘where the engine revolution reaches the maximum, by turing the air screw left and right between 1/4 and 1/2 alternately) At this pont, attention should be paid to the following points 1). there is a certain range inthe opening of the air screw where fast engine revolution can be obtained, (tor instance, the number of ravolutions des not change inthe range of 1-1/2 to 2.0 tr), for better performance you should select approximately 1-1/2 turns. 2) Todetermine the “tully closed” position ofthe air screw, turn the air screw slightly. Excessive tightening ofthe air screw would damage the seat. The position where the air screw comes to a stop should be considered the “fully closed” position. The maximum number of turns inthe opening ofthe air screw must be limited to 3.0. Ifthe ai screw is opened ‘over 3.0 turns, the spring will not work and the air screw can ‘come off during operation of the vehicle. Fig. 16 shows the ‘uel flow curve in relation tothe opening ofthe air screw. ick Revolutions per minute —— ‘Best operating range Air ston opening mea B. - The Cutaway Size of the Throttle Valve (Fig.17) The size of the cutaway of the throttle valve affects the air-fuel ‘misture ratio when the degree of the throttle valve opening is between “V8 and 1/2, especialy in the range of 1/8 and 1/4 opening. As the ‘cutaway geis larger in size, with the throttle valve opening kept unchanged, ar inflow resistance is reduced and causes the amount of air intake to increase, resulting in a lean mixture. On the other hand the smallor the size of the cutaway, the richer the air-fuel mixture will become. Interchange of the cutaway is made, when the low speed fuel ‘system is out of balance withthe main fuel system ira Throwte valve Fig.17 shows the fvel flow curve In relation tothe size of the cutaway. 4» C. - Selection of NEEDLE JET and NEEDLE (Fig.13 & 14) ‘A carburetor with 2 piston-type throttle valve is also called @ variable venturitype carburetor. Ia this type of carburetor, the needle jet and the needle serve to control a proper air-fuel mixture ratio during the so-called) medium throttle valve opening (between 1/4 and 3/4 opening). The right combination of needle jet and needle will have a ‘major bearing on the engine performance at partial load. The jet needle {tapers off at one end and the clearance between the needle and the needle jet increases as the throttle ‘valve opening gots wider. The air-fuel mixture is controled by the height of the needle positioning clip that is inserted into one ofthe five slots provided in the head of the needle. The variation of fuel flow based on the height ofthe pis showm in Fig. 13, eked Generally, itis easier to evaluate and select a needle jet than iis to select a jet needle. The reason is thatthe needle jet sizes are arranged on a linear scale, with each size increasing in increments, (For a thorough explanation of needle jet sizes please refer to Chapter 5.) Jet needles are ‘ot cataloged according to a linear size pattern or a ich to lean scale. The most cffective way to determine the needle jet / jet needle relationship is to visualize the jet needle asa tool for 12560 setting the fuel delivery Tete a oping 8) curve, of the shape of the fuel delivery according to throttle opening. The needle jet controls the fuel delivery rate, either increasing or decreasing the fuel delivery according tothe profile of the ‘needle being used. Sudco suggests that intial, experiments should be limited to changes in needle jet size. Once a satisfactory size has been identified, experiment with needle cip position to obtain the best driveablity and rol-on performance. If one is working with an 0.€.M, Mikuni carburetor, itis safe to assume that the manufacturer has already selected the proper needle or "fuel curve" for that motorcycle and changing the needle profile vill complicate the tuning process, Once the correct needle jet size has been identiied and it becomes apparent that a change in needle profile is necessary, then refer tothe needle dimension charts in Chapter 5. mea — eae To evaluate the performance ofthe needle et, run the motoreycle in third gear at 1/4 thrott, taking notes on how the engine accelerates from 1/4 to 12 throttle only. The engine should respond cleanly and crisply without sputtering or bogging. It may be useful to try experimenting vith clip positions to decide if a problem isa rich or lean condition. I the engine response is better at a lean clip position, it may be ‘necessary to change toa leaner needle et. Sudco suggests that tis best to use as lean a needle jet as possible, a this component will have the ‘greatest effect on fuel economy, emissions, and general driveability. ta leaner needle jot is installed and there is no negative impact on performance, and no postive effec, continue working inthe direction of ean” until there are negative results and go back up one size. D. - Selection of the Main Jet First, do the fllowing on a flat road, 1) Select the largest main jet (the limit of @ rich mixtore) which ‘can give you the maximum revolutions per minute (the ‘maximum speed). In this case, select the engine speed according tothe dimensions ofthe test cours. 2) Compare the gain in speed that you can obtain by quick acceleration rom a constant speed of 25-30 MPH fo maximum ‘desired speed, by using diferent sizes of main jets. 3) Check the exhaust fumes and read the spark plug (selection ofthe spark plug should be made based on the thermal value that would best suit power output ofthe engine) ‘Next, compare on the racing course, the test results you obtained {rom above, The points tobe checked, among others, are: 41) Smooth and steady operation ofthe engine at as high a ‘speed as possible under varying operating conditions ‘such as shiting ofthe gears, changes in oad conditions, ascending and descending slopes, etc. 2), Sustained operation at low speeds and at heavy engine load. 3) Sustained operation at high speeds (without knocking or seizure). CAUTION: Selection of too lean a main jet may cause ‘severe engine overheating, and subsequent piston seizure. Fig.12 shows comparison of fuel flow curves. The straight line is for Model € main jet and the dotted line for Model A ‘and B main jets. n each model of main jet, diferent sizes. within the range of +10% were tried. Figure 12 75515180General Mikuni Slide Carb Circuitry con, 6. MAINTENANCE A carburetor consists of various precision- ‘machined parts such as jets, needles, valves, etc. Therefore, care should be exercised, when removing jets or disassembling the carburetor for cleaning, 1) Proper tools should be used for disassembling ‘and reassembling of jets. Handle each part =| caretuly to avoid scratches, bending, et. \ 2) Wash the jets and the carburetor property in solvent and blow them outwith compressed alr. 3) For carburetors whose main jet can be replaced from a Gre wom] VN2S] ww] vwso | viloo| vist] wae] vise] van | vine = =| T tinem) | 59~,66|99~ 58) 26~04| 6-94] 26-04 65-74 66-74] 5-78 26-74 len) [isc jst? [2anae | 2e-2a zeae 10 [9-79 | 17-19 | 710 ie ibe a ion is eee leakage oe Float Height information for other peter ers a carburetor designs is listed within the 4) [tis important to maintain the fuel level in the carburetor. a Do not touch the oat arm, when disassembling the carburetor. section pertaining to that carburetor. ‘the Moat arm is bent accidentally, adjust the height of rib to the speciic measurement (eter to Fig. 18). 7. TUNING THE CARBURETOR FOR RACING The maximum output ofthe engine depends on: 1) The amount of air drawn into the cylinders: 2) Whether an air-fuel mixture is delivered tothe cylinders ima proper ratio Since the amount of air that is dravin into the the carburetor vats withthe temperature, the atmospheric pressure, humidity, etc the mixture ratio is also changed. Itis important, therefor, that the ‘uel tlw be adjusted in accordance with the altitude of the racing ‘course and meteorological conditions prevailing, A. - Incoming Air in Relation to Meteorological Conditions The amount of air drawn into the eyinders is influenced by such factors as the altitude, the temperature, the humidity, etc. Suppose that the amount of ar sucked into the cylinders at an elevation of zero is taken as 100 (the temperature and humidity in this case are Considered constant). The amount of air in question decreases in proportion to a rise in elevation as show in Fig.19, Reduction in the amount of air dravmn into the cylinders changes the air-fuel mixture ratio, with the resut that the power output drops markedly. Fig.20 shows the relation between arise in temperature andthe amount of air drawn into the cylinders (inthis case, the atmospheric pressure (elevation) and the humidity are considered unchanged and the amount of ar going into the cylinders at 32 degres F (0 degrees ©) is taken a 100). Inthe case ofthe engine for racing where the maximum, output is constantly called for, itis best to tune up the engine by making a matching test of the carburetor in accordance with the ‘temperature and other conditions on the racing course. @ 500 16007800 2060 Altitude (en) , 0 10 2 30 «0 (c) - a a Temperature = —Cea Troubleshooting & ® General Procedures When tuning motoreycle carburetors, there are several procedures and preliminary checks that will make the tuning ‘and troubleshooting process go smoothly and quickly. res Van 1. In order for carburetors to work propery, the engine must be in good mechanical condition, Al of the folowing parameters should 'be checked in order to proceed with the carburetor tuning ‘A. Compression - al cylinders should be within 10% ‘of each other according to cranking compression. 8. Valve Adjustment /Cam Timing - check valve clearance according tothe factory service manual, consult a qualified technician if there is any question about the cam timing 6. Ignition Quality - adjust point gap and ignition timing according to the factory service manual. Double check the {gap and install new sparkplug prior to any carburetor tuning. D. Air Filler Quality - Check to see thatthe air iter is clean and that all baffles and snarkels are in place, or have been removed as necessary for increased airflow. In any case, the air box /air filter dimensions should be finalized. Exhaust System - Install all mufflers and bales. ‘Double check all silencer packing and battle instalations. Finalize all exhaust system specifications before moving on to the carburetors. Jetting can vary dramatically according to ‘mutter /battle selection. 2, All fuel delivery circuits operate according to throttle position, eeNeer In order to determine which circuit to tune, one must know the throttle twrornue vauve —— Pr seers veaTe Bort ra dere “aa — Il hich circuit to tune, Sudco suogests the use ofa throttle index on the (ror aR, puor rT twist grip to track the exact throttle opening ofthe carburetor See Throttle Index . ‘A. Place a peceof masking tape across the trot housing adjacent 4. Altitude and Temperature {eet gis so at tt lve or he rei postion. ‘The purpose ofthe carburetor is to mix air and fuel in a specific B. Install colored push pin or sewing pin int the trate ari rai, by mas, in order to present a combustible mixture to the engine Mange adjacent to the masking tape. Adjust he throttle cable Carburetors are general exibieinstruments when used to mix ai and ‘free play to near zero. fuel in the proper ratio and will compensate for small changes in air With the tote closed, make a “O” mark onthe masking tape density, Is when te altitude or temperature becomes extreme that i adjacent tothe pn head on the thot Mange. wl be necessary to et according to atmospheric conditions. ‘D.Open the throttle all the way and make a "W.0.7" mark on Teitustiog ope adfncen i a pi head. ‘tude and temperature are important factors to consider when tuning carburetors for peak performance, as they directly affect air density, Notes shouldbe teken regarding alitude and temperature ‘changes as they occur in order to determine which way to go with ‘carburetor adjustments, , Using a tape measure, divide the distance between the {wo marks on the tape into quarters and make marks for ‘each trate opening on the tape. (0, 1/4, 12, 3, W.0.T.) F. Ride the motorcycle and make mental notes regarding ‘the carburetion according to the throttle index. Ifa problem Because ar is a gas, its density is directly affected by altitude, Pc atures tesymptans lc spo. Lie a ray es eon wl rhea tote rate psion ce ae a iar Gende toe whee Yo oe 3. Work in progression from 0 throttle through full throttle. how weather pater develop in your ring are ony onto cea The pease ah ee ae Le at ae care Te Bk ax et i 23 zd cant im compensa Tasos, system delivers fuel at all throttle settings, therefore, the tuning of the pilot circuit will nave some influence on the decisions to be made regarding the main circuit there is any question about the jetting of ‘he pilot circuit t should be addressed fist. After the pilot circuit has been optimized itis then possible to accurately evaluate the main circuit and it’s related components,10 Troubleshooting & General Procedures Because air density changes according to atmospheric conditions and fuel density does nat, it becomes necessary to ro-et the carburetor According to changing attude and weather conditions. As the density or mass of ar changes, it becomes necessary to change the mass of fuel ‘mice withthe ar by changing the jets which meter the fuel Altitude affects air density the most. All other conditions being ‘equal, as the elevation nears zoro (sea-level), the air density will be greatest and the engine wil require the richest carburetor settings that ‘wil ever use. As elevation increases, the air density becomes less and the engine will require leaner carburetor settings in order to maintain peak performance. Generaly, an engine which has been tuned correctly for sea-level will not require jetting changes until about 2500’ elevation Temperature also has an affect on air density. As air temperature nears freezing (32 degrees F), the density of air will become greater. Conversely, as temperature rises toward100 degrees F, air density becomes less. AS ar temperature decreases and alr density becomes Areater, the engine will require richer carburetor settings in order to maintain peak performance. Generally, an engine which has been tuned correctly for room temperature (72 degrees F) will not require jetting changes untl the temperature change is about 20 degrees F How To Identify Rich or Lean Conditions Lean Condition - A lean condition is an out of balance air/fuel misure where there is not enough fuel in the mixture to deliver peak performance. The results of lean mixtures can vary from minor driveability problems to overheating and possible severe engine damage. Care should be taken to identify lean mixtures and correct them as soon as possible Typical Lean Mixture Symptoms: 1. Engine acceleration is ator slow to pickup. 2. ttbecomes dificult to apply the tote quicty or the engine picks up speed when the tote is rolled oft 3. The engine knocks, pings, or overheats. 4. The engine suges or hunts fora stable R.P.M. white cruising at par trate 5. When the pilot circuit isto lean there wil be popping ar siting in the carburetors asthe tol Is opened. Sometimes there wil be popping or bactires in the exhaust system on engine deceleration after the throttle has been closed. 6. Engine perormance improves in warmer weather conditions, o engine rans poorly in cold weather. 7. Engine performance worsens when the ar fiter is removed, Rich Condition ~ A rich concition is an out of balance ar / fuel ‘mixture where there is too much fuel in the mixture to deliver peak performance. A rich condition will result in excess carbon deposits within the combustion chamber and exhaust system, decreasing the lite of the engine and related components. in addition to poor fuel economy, a rich running motorcycle will pollute excessively and ‘contribute to environmental problems. Typical Rich Mixture Symptoms: Engine acceleration it at, uneven, not crisp. Two stroke engines wil sputer or "4 stroke” and skip combustion cycles. 3. The throttle needs tobe opened continuously to maintain consistent acceleration. 4. The engine pertrms poorly when the weather conditions ‘get warmer, or the engine works beter in cold conditions. 5. Excessive smoke trom the tail pipe, back smoke fom ‘he tll pipe of four strokes. Poor tue! economy. Engine performance improves when air cleaner is removed. 4. When the pilot circuits rch, the engine wil ile roughly 9rn0t return to ile without binging the trot. The exhaust will smell of excessive fel and burn the eye. 9. Black, sooty or fouled spark plugs. Black and sooty exhaust all ‘ines onfour-stokes. Greasy and dppy tal pies on two-stroke© Troublshooting Guide » Carburetor (ea PROBLEM Possible Causes CORRECTION ‘HARD STARTING. Incorect use of choke. Correct use of choke. Incorrect air-fuel mixture adjustment. ‘Set mitore adjustment screw in accordance with owners manual ‘or shop manual instructions. Clogged tel iter. Clean tte. Clogged tow speed fuel ets. Disassemble carburetor and ‘chemically clean. logged vent in tu! tank cap. Unclog vent or replace cap. Float stuck. ‘Remove float bowi, check fea operation, and corect or replace. Float damaged or leaking. Replace float Incorect oat level. ‘Sottoat height in accordance with shop ‘manual specifications Intake air leak. heck carburetor mounting anges {or air oaks Agntion problem. ‘Repair, replace, or adjust a8 necessary. Low eyinder compression. Repair, replace, or adjust as necessary. ‘POOR IOLE OR STALLING. {le speed adjustments) set too low. ‘Adjust idle RPM in accordance with specifications in owner's manual ‘or shop manual. {dle speed adjustments are unequal Equalze thot stop settings. (win and mutt-carburetor models using Individual trate stop adjustments.) Clogged idle & low speed air bleed, ‘Disassemble carburetor ‘and chemical clean. All causes listed under “HARD STARTING. ” "DLE MIXTURE ADJUSTMENT {te speed set too high. ‘Adjust idle speed in accordance |S INEFFECTIVE, CARBURETOR with speeiction in owner's manual ‘DOES NOT RESPOND TO MOVEMENT ‘or shop manual. OF THE IDLE MIXTURE SCREW. Clogged low speed air bleeds. Disassemble carburetor ‘and chemically clean. ‘Damaged mixture adjustment needle. ‘Replace mixture adjustment needle. ‘Mixture adjustment needle “0” ring is at sealing (models using “0” ring). Damaged mixture adjustment needle seat All carburetor problems listed under “HARD STARTING.” Replace “0” ring. ‘Replace carburetor. nCarburetor Troublshooting Guide 12 PROBLEM POSSIBLE CAUSE CORRECTION ‘SLOW RETURN TO IDLE. lle speed set too high. ‘Adjust idle speed in accordance with specificaions in owner's manual or shop manual. {dle speed adjustments are unequal (twin __‘Equalize throttle stop settings. and molti-carburetor models using individual trate stop adjustments). Throttle valve sticking. Clean and inspect throtle valve and Throttle linkage sticking ‘return spring. Replace as necessary. Clean and inspect throtle linkage and return spring. Lubricate, repair, or replace as necessary. Throttle cable binding Correct routing or replace cable as necessary ENGINE SURGES WHEN Incorrect alt-fuel mixture adjustment Low speed - Low speed jt size change. ‘ATA CONSTANT SPEED. Intermediate-Jet needle height adjustment. Vacuum piston sticking. Clean and inspect vacuum piston and return spring. Replace if necessary. ENGINE DOES NOT DEVELOP Incorrect use of choke. Correct use of choke. FULL POWER, OR MISSES ‘ON ACCELERATION. Clogged air cleaner. Clean or replace. Incorrect air-fuel mixture adjustment Low speed - Low speed ja size change. Intermediate - Jet needle height adj. High Speed - Main jt size change. Throttle valves not synchronized ‘Aajustthotite vaive synchronization. (models with two or mare carburetors) Clogged twel titer. Clean tite. Clogged tue ets. ‘Disassemble carburetor and chemically clean. Clogged air bleeds. ‘Disassemble carburetor and chemically clean, Fuel jets laos. Tighten fuel jets. Fuel jet “0” rings leaking Replace “0” rings. (models using “0” rings). Float stuck ‘Remove float bowl, check Hoat operation, ‘and correct or replace. Float damaged or leaking. Replace flat. Incorrect toat level. ‘Set float height in accordance wit shop ‘manual specification. Vacuum piston sticking. Clean and inspect vacuum piston and return spring. Replace if necessary. Vacuum piston diaphragm ruptured. Replace vacuum piston assembly Ignition problem. ‘Repair, replace, or adjust as necessary. Low cylinder compression. ‘Repair, replace, or adjust as necessary.TM Series Flat Valve Carburetor ‘Mikun’s original flat valve (tat slide) carburetor, the TM Serias blocks which help create a smoothbore effect. The high velocity ofthe Carburetors provide significant performance improvements over older airflow means a stronger vacuum at the needle jet, providing more ‘design round slide carburetors. ir flows faster and smoother through __precise metering and better throtle response. the TM Series venturi due to the fat side configuration and the jet Ower Try wise Barut, coe fee ooror7 Twat 4/042 130 vnz2210 15 832-30008 3.9 1-023 vM28-418 4/042 180 ya2/210 15 832-3300125 None or-026 © TM32-1 4/042 250 © VM2/21045, 832-3901240 None 001-033 TM34-2 4/042 280 VM22/210 50 832-39012 4.0 ‘None 001-038 TM36-2 4/042 280 VM22/210 50. 832-43002a 4.0 ‘None 001-060 TM38-85/47mm* 4/042 230 © vMza/ei0 225 832-490104.0 None 01-061 TMS8-86/44mm= 4/042 230 vMz2/210 225 832-4301040 None 00-032 TM3-8012N100604 127.5 v2arda6 3735, Pilot ir Jet. None “Spigot 0.0, Power Jet Kits Special set TM Series Flat-Valve Carbs Use the folowing part numbers when ordering a special The TM Series bodies FLAC LA) ae int Sites taies | pamper wear Pmganen | SR “Spigot 0.0,™ ® Mikuni Needle Jets eT Needle Jets ‘The needle jet is the main fuel passage to the main bore (venturi of the Mikuni carburetor. Depending an the inside diameter ofa specific needle jet, this will also affect the function of the needle, Therefore, needle jets and neadles act together as the main system in controling the amount and mixture of the fuel which is drawn in mid-range (4-314) throttle operation Two Basic Types of Needle Jets ‘PRIMARY TYPE __ BLEED TYPE 7, qv Primary Choke Type For Mikuni Series #224 LEAN 20 ca} ARO ANS 88-0 BBS co-0 RICH C5 Note: Letters Z, AA, BB, and CC are sizes in increments of 050mm, Numbers 0 & 5 are sizes in increments of 25mm, 159 Om RS P 30 36mm Spigot Using the application chart located on page 7, itis noted that | 168 O-DthuR-S e si Slact carn needle jets require a specitc type of main jet because there are | 162 NOt 0-8 B Stim Senko ‘wo types of main jets (4/042 & N100/604) that have different fuel low | {7 OO nu P em Flange Tale characteristics. Also, nedle jets are available nt only in types, but | ye rgmuae 8 oeraeeee Series and sizes. Use Mikuni series numbers for style of the need jet. | 176 Nonuae 8 20 aera Spigot Ther ies (inside diameter sie) within each series are listed according | iyo Nomuae P 2mm spigot to.aleter-number combination. The letter shows the inside diameter} jg8 — Q-otnvas P 32mm Flange, Kawasaki Suen increments of 50mm. 12 NOthwOS P 26mm Fiange 193 Nomuos P 2mm Flange For example the dference between P-2 and Q-2 is that the inside | 205 O-d tw 08 p 234mm ange siameter of reece jet size 0-2 is 0mm greater than P-2 21 NotmuOs ° Kew 2507350750 24 FigueB P 40-44mm Spigot The number shows the inside ameter siz in increments ot 010mm. | 235 O-Dthu oe ° ‘30mm Fange 247 P&Qonly P Yamaha 250, 2400 T400 For example the diference between P-2 and P-4is that the inside | 258 0.8 Pony 8 Yamana TT, SR, XT500 lameer of meade jt size P-4 is 010mm greater than P-2. Suzuki, SP, 63560 65750850, Exception: (6) is measured as an inerement increase of 005mm, aw K2650,/1000 For example, the diference between P-4 and P-5 is that the inside | 261 N8muas 8 ‘M29 and V3 ameter of needle jt size P-5 is 005mm greater than P-4 Smoothbores 389 O-OthuRS P Tu32, 34, 36,38, 41 Pro-Seris and Flt-Side 499 p-2thwa4 8 THB Fat Side Smoothbore 568 O-6ihuP-8 P S34, 36 Racial FS Smoothbare 568 Y-omnwz6 P S39, 40 Radial FS Smocihioore ‘Needle Jet Orifice Diameters Bote oar nS 4 5 6 7 8 2 2550 2555 2.560 2565 25702575 «2580 2585 «2500 2.595 2600 2605 2610 2616 «= 2620-2625 2690 216526402645 2650 2655 © 2.660 2665 ©2670 ©2675 «2880 «686 ©2690 2695 2700 2705-2710 a718 27202725 «273027352740 7A, 61Mikuni Needle Jets 4 Needle Jets 7 ‘Sizes Series ——> 159 166 169 m 172 115 176 Lean N-0. 003-249 003-271 003-324 Neo 003-250, 003-272 003-205 Ne 003-200 003-254 008-273 003-326 N6 003-201 003-252 003-274 003-327 NB 003-202 003-253 (003-275 003-328 0-0 003-203, 003-207 003-254 003-276 003-329 02 003-204 003-228 003-255 002-277 003305 003-830, 0-4 003-205 003-229 003-256 002-078 003-294 003-331 0-5 003-543, 003-545 003-257 0-6 003-208 003-230 003-258 003-279 003-295 003-307 003-333, 08 003-207 003-231 003-259 003-280 003-298, 003-308 003-334 Po 003-208 003-232 003-260 03-281 003-309 903-335 Pa 003-209 003-283, 003-264 003-282 003-208 003-310 003-836 Pes 003-210 003-234 003-262 003-283 003-311 003-337 Ps 003-211 003-235, 003-263, 003-312 003-338 Pb 003-212 003-236 003-264 003-284 003-313 003-339 PB 003-213 003-237 003-265 003-285 003-314 003-340 0 003-214 003-238, 003-266 003-286 003-315 on 003-215 (003-239 003-267, 003-287, 003-342 a4 003-216 003-240 003-268 003-288 003-343 O5 003-217 003-546 06 003-218 003-241 003-269 003-289 003-344 a8 003-219 003-242 003-270 003-290 (003-345 Reo 003-220 003-243 003-291 Re2 (003-221 003-248 RS Rel 003-223 003-245 RS 003-224 003-246, 003-349 vy RG 003-225 003-247 Rich R-8 003-226 003-248 Sizes Series —> 182 183 188 192 193 196 235 Lean N-0) 003-352 003-372 003-424 ND 003-353, 003-373, 003-425 Ned 003-354 003-374 NG 003-355, 003-375, NB 003-356 003-376 03-414 0-0 003-357 003-377 003-439 on 003-358 003-378 003-394 003-413 003-440 03 O-4 003-379 003-395 003-441 05 003-442 6 003-360 003-381 003-417 003-432 003-443, OB 003-361 003-382 003-398 003-433 003-444 Po 003-362 003-383, 003-399 003-419 003-434 Pe2 003-363, 003-384 003-420 003-435, Peg 003-385, 003-421 003-436 P6 003-365, 003-386 003-422 003-437 003-503, PB 003-366 003-387 003-404 003-428 003-438 003-450, a0 003-367 003-388 003-451 a2 003-368, 003-389 003-452 a4 003-369 003-90, 003-453, Y 36 003-370 003-391 Rich 0-8 003-374 003-392eed 4 Mikuni Needle Jets Needle Jets ‘Sizes Series > 247 258 35, Tt cy Lean 0-0 008-522 008-570 003-592 02 003-523 03-571 003-533 o4 003-324 03-572 003-534 08 09-573 (03-585 08 00-526 03-574 003-536 P 003-510 008-527 008-575 08-537 P2 003-511 008-528 08-578 003-538 003-806. Pa 003-512 003-528 003-577 003-539 PS 003-513 P6 03-514 003-530 08-578 P38 003-515 008-531 03-579 003-549 003-600 0 003-516 008-580 003-610 2 003-517 08-581 008-611 a4 003-518 03-582 003-612 06 003-520 00-583 08 (003-521 00-584 Ro 003-563 03-585 R2 (03-554 03-588 Re 006-555 003-587 Yo oR6 (08-566 003-588 Rich RB 008-587 005-589 003-589 Needle Jets (contiwes) Sines “Series —> 568 (RS39-10) Series ——> 568 (RS34-35) Series =——> ‘224 T van yo 003-663 06 003-650 05 003-560 \ Y2 008-664 o8 003-651 0 003-495 Ne 008-665 Po 08-652 25 003-496 YS 008-668 P2 003-653 Ano 008-497 v8 009-667 Pa ‘03-654 AAS 003-498 20 008-668 P6 008-855 86-0 008-499 22 008-669 Pa 008-656 88-5 003-500 voz 008-670 coo 008-501 Rich (26 008-671 cos 003-502 Throttle Valve (rst atomic cas or No OF cat tet So st orb motel soci Sato part be) Part Carb Slide Idle Screw Guide Pin Cut-away Number ‘Application Material Location Groove Width Sizes Available 28156 26-28 Spigot Brass Lett 2.05mm 15,20 vor176 30 Small Body, Brass Left 2.05 1.0 thru 3.5 M3265 30, 32, 34 Spigot Brass Right 2.60 15 thru 3.5, vagart10 30,32, 34 Spigot Brass Left 260) 1.01nTu3.5 M6/36 36 Spigat Brass Left 3.05, 15 thru 3.5, ‘yMg6/39 36 Spigot Brass Right 3.05, 30,35 ‘yge/24 38 Spigot Brass Right 3.05 10thru 3.5 vyMa/s2 38 Spigot Brass Lett 3.05 15 thru3.0 ‘yano2 40, 44 Spigot Alum, Left 3.05 05 thru 4.0 yaaa 40, 44 Spigot Brass Lett 3.05 1.5 thru 4.0 32-99012 TM32-34 Alum, Lett 40 -892-49002 TM36, 38 Alum, Lett 15 thru 5.0 1892-49011 ‘TM8-85, 86. Alum, Left 25 tnruas 999-892-014 TNXG5, 38 ‘Alum. Left 25 thru6.0 999-832-017.16 TMS38, 125 Alum, Lett None 960-892-017-1H TMS38, 250 Alum Lett None NOTE: Brass sides are chrome pated. Aluminum slides are anodied,Xylan or Nickel-pates,Mikuni Jet Needles Quick Reference Chart for Needle Selection (average Performance Chart) Note: The following listing of neadles are simply the average performance of a needle between 1/4 and 4/4 throttle opening. Needles are constructed such that a given point on a needle, (for ‘example, at 3/4 throttle opening), the needle maybe fount to perform vicherat this given point when compared to the same given point an another needle, but according the the average performance chart, the needle should perform leaner. For examplk average Performance chart leaner GDH DS IA) ' RT SFI6 D-5 (B) ' Richer oR ee ALD-5 (A), the taper diameter is 1.916, at D-6 (b), the taper is 2.040; the taper diameter at D5 (A) is smal than D-5 (B). At this ‘iven point of throttle opening (8/4), needle 6DHA wil run slighty richer than BFAB, but the average performance wil stil be that 6DH4 willbe a leaner needle because I will perform leaner at more given points than a 6FUB. Consequently, if you are concentrating on a specific throttle opening for competition use, be certain to check the ‘taper diameter at that point of throttle opening, Fora more detailed and comprehensive explanation ofthe various needles as to their taner diameters at given points, see [NEEDLE TAPER DIAMETER DIMENSION CHARTS. THE QUICK REFERENCE CHART FOR NEEDLE SELECTION vas prepared by measuring the needles as to their diameter at iven points. Given points are 10mm apart trom each other. By computing the diferent measurements and arranging them in order of taper thickness or thinness, three categories for application of needles were determined. Category | - Competition. For example, motocross racing and desert racing where mid-range throttle operation is vital. Category Il - Racing. For example, Road racing, where 3/4 to full throttle operation is vital. Category Ill - Overall. For example, Street riding, where the full range of throttle operation is required. NEEDLES #4 SERIES Cn oo veaven 1 408, 4°3) 4P3 2 DHT 408 408 3 4066 403 403 4 4p 4Fi0 4066 5 403 4066 4DH7 6 46 46 4F10 7 410 DHT 465 8 415 4Fi5 4FI5 9 4e14 a 4Et 10 413 4u3 4ui3 "1 als aut 413 2 4L13 4s13 4a toner 13 aunt 4U6 46 NEEDLES #5 SERIES CE OVERALL uae 4 506: 54 504 2 50120 506 506 3 5c4 505. 505, 4 SENS 50120 50120 5 59 501 SFB 6 5F18 SFB 501 7 SOP, 5FI6 SENS 8 SFL14 Sra 53 9 53 53 5EH7 10 SEHT BES Sf i SFLT SEH? SOP 2 505 ‘SDH21 SFLt4 13 5E13 SFLIa SFT “4 5u1 SFL 5E13 18 516 5E13 SFG 16 501 50P7 5DH21 7 59 59 59 18 SFI6 56 516 19 SDH2t SLI BL racer 20 SFI2 512 5FI2 Please Note: Many of the needles listed in the charts above are ‘no longer in production. We have listed them for reference only.eae Mikuni Jet Needles NEEDLES #6 SERIES ‘COMPETITION RACING Co NEEDLE TAPER DIAMETER a ao ie Eh ee DIMENSION CHART (A) ; oy OO 4 GFE 6OH7 DHT (a)=Needle Length (mm) 5 63. 65. 6DH4 (b)=Length between points (x) and the taper point (Y) i gy «6S it 6F9 ‘DHA 6F8 t=10mm 8 605 6Fo 6L1 (220mm 9 6FS BFI6 GFE 330mm 10 6ul 6CrI GCFI 4=40mm a 6DP1 6DH2 6FS 5=50mm 2 8 BR OR te ett 1-4-2, 4-8 ato ata taper tantra tae phon ee are a Rahs : 2 8 @ a a ee ee ao, | OO NEEDLES #7 SERIES eee re rer a ener sere ; & ® 8 ro: ot 6hMikuni Jet Needles Jet Needles Series Type Application , 4 "ALB Carburetors ‘The Jet Needle controls the fue mixture inthe mid-range (14- mn baie 3/4) throttle position. The taper of the needle determines the amount EEO A BS Fane Of fuel. For example: the thinner the ciameter ofthe needle, the mare = ai Sa wae fuel wil be drawn. The thicker the dameter of the needle, theless fuel Seonganmeee can be dawn. 6 30mm-38mm Spigot Two Types of Needles: a 401mm an 44mm Spigot ” 1 and HS Carbs Taper Point 1-1 through 0-6 indicates diameter (mm) at each point. Double Taper Type Aa || 2B | DPR, | BS, BF" |S Oe L WORE [e23_| PHO Ran | Bain [anes [2206 [2000 [ree ow ow oro | 623 [aso [este | 2sis [2ars [2210 [1900 [1078 sort [ons | 295 [2512 | 2512 [2420 | 2240 friars [i710 tape a) Taper! @) FIG | 623 | 35.2 | 2.505 | 2.505 | 2.505 | 2.376 |2.040 |1.606 ons | 623 | 220 [2si2 | 25i2 [2ase [2206 [ioe [aor Needle Taper Diameter Dimension Chart ai1_[ ees | 70 [zie | asia [asre | 208 |ra2s [raia D+ through 0-5 indicates diameter (mm) at each point A | 8 | o1 | 02 | 03 | 04 | 05 ‘ae [0S_ [280 _[zare aors |asas [ater _| 1908 aon7_[503 [230 [ase | ste | 236 | 2098 [1.700 ana_|s02 [240 [asia [asia | 2230 | 1.800 | 1.400 ‘aus [sos [2as [esis | 2sts | 2rze | 1.660 [1.190 am [ars [213 [asia [2606 [2tee [1.776 D+ through D-6 indicates diameter (mm) at each point. eort7| 623 | a2.1 [2516 | 2516 [2518 [2972 [1ax [ita oni_[ 623 | 370 [2ta | 2514 [asta |az7e [1672 |1.058 ort | 623 | ena [asit | 2511 [are [asta |i.7ae [tors eons | 623 | 255 [2520 | 2520 [2.400 [2258 [1918 [1575 Son7 | 622 | 285 [2si6 | a5ie [2505 | 2916 [2000 [1.606 sone | 622 | 203 [2598 | asse [206 [2208 |1az7 |tae7 erita | 621 | 267 [2598 | 2530 [2506 [2203 |1.6%9 [1216 eri | 622 | 198 [2505 | 2590 |245t [2208 [1.970 |16to orto] 624 | 265 [251 | 261 [eas [226 [tse | 0 eri | 642 | ae [250 [24s [ome [22a [ta7 [iro sousa | 647 | 263 [251 | 2st [aes [20d [tes fran A} a|o4| 02 | 03| 04 | 05 | 06 sra_| 500 | 274 | 2510 | 2519 | Dato [2.195 | 1063 sestt | 603 | 285 | 2515 | 2515 | 2515 [2.241 | 1.009 [1.420 srutt | 603 | 282 | aste | 258 | 2.490 [2.175 | 1.740 [1.256 srite| 500 | 280 | 2520 | 1520 | 2.440 | 2170 [1.705 sez | sao | 200 asts | 2518 | 2.400 [2.170 [2.170 [1.795 sop7 | 76 | 264 | asta | 2512 | 2.440 | 2259 | 1.580 56_| se0 | 275 | 2518 | 2518 | 2.340] 1.00 | 1.450 sut_| 580 | 270 2518 | 2518 | 2390 | 111 [1297 sua [580 | 27.0 | 2522 | 2520 | 1.432 | 1.905 | 1.505 Needle Taper Diameter Dimension Chart 4 | 8 [01] 02/03] 04] 05 | 06 [07 ‘ons| 722 74] 2.96 | 2.98 | 294 | 276 | 248 | 208 | 1.72 ret_| 723] a1] 299 | 299 | 299 | 290 | 258 | 228 | 202 76 | 723| 290] 3.00 | 3.00 | 295 | 2.68 | 241 | 214 | 1.07 rows) 725| 281] 2.98 | 298 | 296 | 200 | 247 | act | 1.76 row| 753 31.6] 299 | 299 | 299 | 284 | 266 | 227 | 1.92 0-1 through D-6 indicates diameter (mm) at each point, a _ A|8| ¢ | 01) 02 | 03 | 0-4 | 05 | 06 4 we aa al al Pa ee ol, or en eg ees satis oe es GFB | 62.3) 34.0 | 21.5] 2.512) 2.512 | 2.386 | 2.214] 1.945 | 1.688 ae 40: 50. * eF16| 646/312 [18.4] 2520] 2404 | 2.400] 2201 [1.941 | 1.679Mikuni Jet Needles sive cats Jet Needle No. Applications ‘Needle Diameter-Betore Taper (mm) Al Fuel Ration ort mois TWG8 FLATSLIDE 251 LEANER: eras 02-349 251 BF 02-12 250 60Ps 02-341 v RICHER ees. 60 07-077 TWXGE FLATSLIDE 260 LEANER: 59 007-075 259 58 007-075, 258 57 007-074 257 55 007-073, 258 55 007-72 255 54 Ou7-071 254 53 007-070 Y 253 RICHER GENT 58 007-056 TMXSS FLATSLIDE 258 LEANER 57 007-085 257 55 007-054 256 55 007-053, 255 54 007-052 254 53 007-051 253 52 007-050, 252 51 007-049 y 23 RICHER eeovi2- 60 007-089 1836-7. 78 260 LEANER 59 007-088, 125ce 259 53 007-087 258 57 007-096, 237 55 007-085 Y 258 RICHER eocvos-so 007-048 1MS36-77, 78 260 LEANER 59 007-047 2500 259 58 007-045, 258 57 007-045 257 53 007-044 258 55 007-03 255 54 007-042 y 254 RICHER 90zi01 STO 007-085 834-96 250 LEANER 902403 007-037 SMOOTHBORE 249 x 902H04 007-038 248 ricer 9oHvO3 ST on7-020 S940 298 LEANER 9cH¥05 7-022 SMOOTHEORE 298 9CHY08 07-023 297 RICHER ‘90H 10-89 (@CHYO) STO 838-40 299 LEANER 8 295 95 295, 9 y 294 % 290 RICHER 90,01 STD oo7-015 sao. 297 LEANER sosv0s 07-017 SMOOTHBORE 298 sorvoz 007-016 295 RICHER anpvores 007-088 sa 42 Leann 8DDvO;-O7 007-082 NEEDLES S0DVO1-96 STD 007-081 soDvO1-95 007-080 ici ro Oplion-TMS38 Needles (tor 125 & 250 ct Engines without Main Jets thru 1992 Each kit contains a selection of 5 different needles) KITNO, [NEEDLE DIAMETER ‘AVFUEL MAIN JET EQUIVALENT | SUDCO PART 125.60 TMSIN25056 256mm richer 400, 390, 380,70, 60 007-091 TMS-INI2557 257mm 400, 390, 380,370,360 07-092 TMSINI2558 28mm leaner 400, 390,380,370, 360 097-095, 250.60 ‘TMS-IN250057 257mm sicher 980, 970, 360, 350, 40 007-095 TMS-IN25088 258mm 380, 370, 360,350,340 07-096 ‘TMS-IN250859 259mm leaner 380, 370,360, 350, 340 007-097 NEEDLE PART NUMBERS 400) (G80) (30) (70) GED) {@50)_(70) (350) EO) (940) 125 cc = JBGEL 11-15 Wor 12, 13, 14, 15 -(400-360) —250.c0-J8-6 CEMOT-05 Ot or 02, 03,04, 05. (380-240) Important Note 1 our uta! covet ting sng a TMS Car a win he guideline abl, you may achive improved patemance wth he pro-ain ki, ample: TMS 8 ath GDGYOUS7 and S60 main choose TMSN2S0S7 6eT Mikuni Main Jets ‘Main Jets Small Small Large vinnie es ete aimcnueatete lt | mate | amen | ae atid aeStontine ey am eset | Woeeeso | Ges ane | ie os Eiitiehcimmetiwed eatacen | wus % | mas Bs | mene Brereton ize | mises | otis. : eels | Beles | Mee meant. Te a 004-229 75 gia 62.5 ae 625 004-230 80, 004-271 65 166 65 492 amet s0n — | A | Lame, ue thon | wea sis | Grier enemy - a | os | comes ee Fe gee 8 | suas ms | ties ie eee nes 105 pe 715 we LB eels | tens | Sett wou Lae raund 50921080 our m3 | meze es | oui is oe Orth ipeae ti | tree | et se ‘171, 188, 196 (9, 50, 62.5, 55, 004-240 130 004-281 90 004-176 90 gas oe | oe | oe eels | Ries | me i014 ‘Small Hex +#50-#200 in 004-243 145 004-284 75 004-179 97.5 22s,. ees | tts | Be 004-245 155 004-286 102.5 oe 102.5, a oe | oe | ans 102/221 ‘Small Round +#30-#190 in 004-248-170 004-289 110 004-184 110 Sallam, poet oes | Bee ie. | Set, x or ag om ® BS see pees gee | gets | Suri. al aR a 208.099 Press in (See Mikuni Catalog) ore eee | {ate model 004-254 200 004-295 125 004-190 125 Ducati Cv 004-296 127.5 004-191 1275 Yamaha CV 004-297 130 004-192 130 ees | meee ie ees | ee Hex 004-300 137.5 pan 137.5 cee | me en — ee ootsoe 1425 | oodter 1425 0807155 04-100 180 004-126 410 004-203 145 Oo4-198 145 mess | pee ae a, | eS! cele | oe eo es oe Bisse teas | tan en 00407470 04-103 195 (004-129 440 ee ei a a ae mise is| tgs covtre 80 04-105. 210 ond31 460 ener ares co4-077 85 004-108 220 004-132 470, aoe. | oo Pitan cites, | fe gursio seas | auame_Ie a a ouesit iss) | tibet 04-080" 100 ‘004-109-250 (004-135) 500 Doesigoeta (oieemeinn ma west am | onze 004-082 110 004-111 270 004-139 540. 004-315 175 004-210 175 So Se Mee Rae | eae 004-084 120 004-113 290 004-143 580. 004-317 180 004-212 180 ee ean ea eae | Reem a ae mes | mee cS cee ume | penne 004-088 140 004-118 330 004-148 650 004-321 190 004-216 190 004-089 145. 004-119 340 004-149 660. 004-322 192.5 004-217 192.5 (004-090 150 004-120 350. 004-150 680 004-323 195 004-218 195 TLE AD aD amos | Beem 004-092 160 004-122 370 004-152 710 004-325 200 004-220 200 004-093 165 004-123 380 004-153 720, 004-201 202.5 008-094 170 004-124 390 004-222 205 04-203 210Mikuni Pilot Jets Pilot Jets vm22/210 #10-#95 Most Mikuni Carbs. Boy ‘to #30 by “5” from vm2g/213 (#15-#40 in. 211972 VM28/486 412.5 - fu 6 ee 2 [ili Chotes) RS38mm vm28/1001 415-865 in 22 Flange (1000cc, increments of 2.5, 2 cycle,Banshee, RZ,Blaster Yam) BS30/96 +#30-460 OEM CV Carb increments of 2.5 q vmz2/210 VM28/100 1 (continues) ‘Order No. Size ‘Order No. ‘Size 004-001 #25 004-045, #45, ae ie Ri is ee, me ae is Be ae Bee 004-007 $27.5 VM28/486 004-008 #30 Order No. ‘Size ae ae am ue 004-012 #50. 004-030 #20 004-013. 995 004-031 #225 #60 vMN28/213- #65. ‘Order No. ‘Size 004-020. #75 Size 004-022 822.5 #325 004-023, #25, #35, 004-024 #30 #375 004-025, #35, #40, 004-026. #40 #425 vm26/1001 #475 Order No. ‘Size #50. #5 #525 EA Air Jets [Meters the air low through the passage to and into the needle jt. It acts as a fine tuning component in regulating the fuel-air mixture, ‘This is especialy important winen a bleed type needle jet is used a3 Mikuni No. Application BS30/907 26 thru 44mm Spigot beans fey BS30/97 002-151 06. 002-152 O7 002-154 09 1.0 if 1.2 13 m 15 ' VW " 8 #165 #170 002-170 #200 002-171 #210 Starter Jet (Fits TM32 thru 38) 004-400, #15 re = 004-402 #20 ie a PEGA PLOT ETS ol Wika N151.067 N224.103 (OEM for Yamaha YZ motoreycles, original equipment in Mikuni TMX ‘carburetors, Sizes 30 thru 65 in increments of 2.5 5