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    Carburetor 1001

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    faiz_krr

    Carburetor 1001

    Post by faiz_krr on Tue Sep 08, 2009 11:52 am

    assalamualaikum dan salam sejahtera..


    aku buka thread ni nak berkongsi tentang carb..harap dapat memberikan sedikit kefahaman untuk kita semua..

    ni aku petik dari web..IAN WILLIAMS TUNING..www.iwt.com.au

    Mikuni Motorcycle Carburetor Theory 101

    Motorcycle carburetors look very complex, but with a little theory, you can tune your bike for maximum performance. All carburetors work under the basic principle of atmospheric pressure. Atmospheric pressure is a powerful force which exerts pressure on everything. It varies slightly but is generally considered to be 15 pounds per square inch (PSI). This means that atmospheric pressure is pressing on everything at 15 PSI. By varying the atmospheric pressure inside the engine and carburetor, we can change the pressure and make fuel and air flow.

    Atmospheric pressure will force high pressure to low pressure. As the piston on a two stroke engine goes up (or goes down on a four stroke engine), a low pressure is formed inside the crankcase (above the piston on a four stroke). This low pressure also causes a low pressure inside the carburetor. Since the pressure is higher outside the engine and carburetor, air will rush inside the carburetor and engine until the pressure is equalized. The moving air going through the carburetor will pick up fuel and mix with the air.

    Inside a carburetor is a venturi, fig 1. The venturi is a restriction inside the carburetor that forces air to speed up to get through. A river that suddenly narrows can be used to illustrate what happens inside a carb. The water in the river speeds up as it gets near the narrowed shores and will get faster if the river narrows even more. The same thing happens inside the carburetor. The air that is speeding up will cause atmospheric pressure to drop inside the carburetor. The faster the air moves, the lower the pressure inside the carburetor.


    FIG 1


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    faiz_krr

    Re: Carburetor 1001

    Post by faiz_krr on Tue Sep 08, 2009 11:55 am

    Most motorcycle carburetor circuits are governed by throttle position and not by engine speed.There are five main metering systems inside most motorcycle carburetors. These metering circuits overlap each other and they are:
    * pilot circuit
    * throttle valve
    * needle jet and jet needle
    * main jet
    * choke circuit

    The pilot circuit has two adjustable parts, fig 2. The pilot air screw and pilot jet. The air screw can be located either near the back side of the carburetor or near the front of the carburetor. If the screw is located near the back, it regulates how much air enters the circuit. If the screw is turned in, it reduces the amount of air and richens the mixture. If it is turned out, it opens the passage more and allows more air into the circuit which results in a lean mixture. If the screw is located near the front, it regulated fuel. The mixture will be leaner if it is screwed in and richer if screwed out. If the air screw has to be turned more than 2 turns out for best idling, the next smaller size pilot jet will be needed.


    FIG 2


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    faiz_krr

    Re: Carburetor 1001

    Post by faiz_krr on Tue Sep 08, 2009 11:58 am

    The pilot jet is the part which supplies most of the fuel at low throttle openings. It has a small hole in it which restricts fuel flow though it. Both the pilot air screw and pilot jet affects carburetion from idle to around 1/4 throttle.

    The slide valve affects carburetion between 1/8 thru 1/2 throttle. It especially affects it between 1/8 and 1/4 and has a lesser affect up to 1/2. The slides come in various sizes and the size is determined by how much is cutaway from the backside of it, fig 3. The larger the cutaway, the leaner the mixture (since more air is allowed through it) and the smaller the cutaway, the richer the mixture will be. Throttle valves have numbers on them that explains how much the cutaway is. If there is a 3 stamped into the slide, it has a 3.0mm cutaway, while a 1 will have a 1.0mm cutaway (which will be richer than a 3).


    FIG 3


    The jet needle and needle jet affects carburetion from 1/4 thru 3/4 throttle. The jet needle is a long tapered rod that controls how much fuel can be drawn into the carburetor venturi. The thinner the taper, the richer the mixture. The thicker the taper, the leaner the mixture since the thicker taper will not allow as much fuel into the venturi as a leaner one. The tapers are designed very precisely to give different mixtures at different throttle openings. Jet needles have grooves cut into the top. A clip goes into one of these grooves and holds it from falling or moving from the slide. The clip position can be changed to make an engine run richer or leaner, fig 4. If the engine needs to run leaner, the clip would be moved higher. This will drop the needle farther down into the needle jet and cause less fuel to flow past it. If the clip is lowered, the jet needle is raised and the mixture will be richer.

    The needle jet is where the jet needle slides into. Depending on the inside diameter of the needle jet, it will affect the jet needle. The needle jet and jet needle work together to control the fuel flow between the 1/8 thru 3/4 range. Most of the tuning for this range is done to the jet needle, and not the needle jet.


    FIG 4


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    faiz_krr

    Re: Carburetor 1001

    Post by faiz_krr on Tue Sep 08, 2009 12:06 pm

    The main jet controls fuel flow from 3/4 thru full throttle, fig 5. Once the throttle is opened far enough, the jet needle is pulled high enough out of the needle jet and the size of the hole in the main jet begins to regulate fuel flow. Main jets have different size holes in them and the bigger the hole, the more fuel that will flow (and the richer the mixture). The higher the number on the main jet, the more fuel that can flow through it and the richer the mixture.


    FIG 5

    The choke system is used to start cold engines. Since the fuel in a cold engine is sticking to the cylinder walls due to condensation, the mixture is too lean for the engine to start. The choke system will add fuel to the engine to compensate for the fuel that is stuck to the cylinder walls. Once the engine is warmed up, condensation is not a problem, and the choke is not needed.

    The air/fuel mixture must be changes to meet the demands of the needs of the engine. The ideal air/fuel ratio is 14.7 grams of air to 1 gram of fuel. This ideal ratio is only achieved for a very short period while the engine is running. Due to the incomplete vaporization of fuel at slow speeds or the additional fuel required at high speeds, the actual operational air/fuel ratio is usually richer. Figure 6 shows the actual air/fuel ratio for any given throttle opening.


    FIG 6


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    faiz_krr

    Re: Carburetor 1001

    Post by faiz_krr on Tue Sep 08, 2009 12:09 pm

    Carburetor Jetting Troubleshooting

    Carburetor troubleshooting is simple once the basic principles are known. The first step is to find where the engine is running poorly, fig 7. It must be remembered that carburetor jetting is determined by the throttle position, not engine speed. If the engine is having troubles at low rpm (idle to 1/4 throttle), the pilot system or slide valve is the likely problem. If the engine has problems between 1/4 and 3/4 throttle, the jet needle and needle jet (most likely the jet needle) is likely the problem. If the engine is running poorly at 3/4 to full throttle, the main jet is the likely problem.


    FIG 7

    While jetting carburetors, place a piece of tape on the throttle housing. Place another piece of tape on the throttle grip and draw a line (while the throttle is at idle) straight across from one piece of tape to the other. When these two lines are lined up, the engine will be idling. Now open the throttle to full throttle and draw another line directly across from it on the throttle housing. At this point, there should be two lines on the throttle housing, and one on the throttle grip. Now find the half-way point between both of the lines on the throttle housing. Make a mark and this will show when the throttle is at half throttle. Divide the spaces up even again until idle, 1/4, 1/2, 3/4, and full throttle positions are known. These lines will be used to quickly find the exact throttle opening while jetting.

    Clean the air filter and warm the bike up. Accelerate through the gears until the throttle is at full throttle (a slight uphill is the best place for this). After a few seconds of full throttle running, quickly pull in the clutch and stop the engine (Do not allow the engine to idle or coast to a stop). Remove the spark plug and look at its color. It should be a light tan color (for more info on reading spark plugs click here). If it's white, the air/fuel mixture is too lean and a bigger main jet will have to be installed. If it's black or dark brown, the air/fuel mixture is too rich and a smaller main jet will have to be installed. While changing jets, change them one size at a time, test run after each change, and look at the plug color after each run.

    After the main jet has been set, run the bike at half throttle and check the plug color. If it's white, lower the clip on the jet needle to richen the air/fuel mixture. If it's dark brown or black, raise the clip to lean the air/fuel mixture.

    The pilot circuit can be adjusted while the bike is idling and then test run. If the engine is running poorly just off of idle, the pilot jet screw can be turned in or out to change the air-fuel mixture. If the screw is in the back of the carburetor, screwing it out will lean the mixture while screwing it in will richen it. If the adjustment screw is in the front of the carburetor, it will be the opposite. If turning the screw between one and two and a half doesn't have any affect, the pilot jet will have to be replaced with either a larger or smaller one. While adjusting the pilot screw, turn it 1/4 turn at a time and test run the bike between adjustments. Adjust the pilot circuit until the motorcycle runs cleanly off of idle with no hesitations or bogs.


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    faiz_krr

    Re: Carburetor 1001

    Post by faiz_krr on Tue Sep 08, 2009 12:11 pm

    Altitude, Humidy, and Air Temperature

    Once the jetting is set and the bike is running good, there are many factors that will change the performane of the engine. Altitude, air temperature, and humidity are big factors that will affect how an engine will run. Air density increases as air gets colder. This means that there are more oxygen molecules in the same space when the air is cold. When the temperature drops, the engine will run leaner and more fuel will have to be added to compensate. When the air temperature gets warmer, the engine will run richer and less fuel will be needed. An engine that is jetted at 32deg Fahrenheit may run poorly when the temperature reaches 90deg Fahrenheit.

    Altitude affects jetting since there are less air molecules as altitude increases. A bike that runs good at sea level will run rich at 10,000 ft due to the thinner air.

    Humidity is how much moister is in the air. As humidity increases, jetting will be richer. A bike that runs fins in the mornings dry air may run rich as the day goes on and the humidity increases.

    Correction factors are sometimes used to find the correct carburetor settings for changing temperatures and altitudes. The chart in fig 8, shows a typical correction factor chart. To use this chart, jet the carburetor and write down the pilot and main jet sizes. Determine the correct air temperature and follow the chart over to the right until the correct elevation is found. Move straight down from this point until the correct correction factor is found. Using fig 8 as an example, the air temperature is 95deg Fahrenheit and the altitude is 3200 ft. The correction factor will be 0.92. To find out the correction main and pilot jets, multiple the correction factor and each jet size. A main jet size of 350 would be multiplied by 0.92 and the new main jet size would be a 322. A pilot jet size of 40 would be multiplied by 0.92 and the pilot jet size would be 36.8.



    FIG 8

    Correction factors can also be used to find the correct settings for the needle jet, jet needle, and air screw. Use the chart from fig 9 and determine the correction factor. Then use the table below to determine what to do with the needle jet, jet needle, and air screw.



    FIG 9


    This article was written by, and has been reprinted with the permission of Doug Jenks. All rights reserved.
    smallengprep@yahoo.com


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    wadin

    Re: Carburetor 1001

    Post by wadin on Fri Oct 02, 2009 11:39 am

    good info....aku baru terbaca beb....
    Harap kawan kawan dapat info ini....

    pcq5913

    Re: Carburetor 1001

    Post by pcq5913 on Sat Dec 05, 2009 3:54 pm

    hoh.... xphm aku bahase omputih nih... dolu skolah x habis... bulih alih bahasa x?. aku tgk citer otromen ngan spongebob pun cakap melayu... huhuhu. kalu bulih tolong la jelaskan dalam bahasa MELAYU..


    (aku x reti bahase omputih ni..) What a Face bom

    duke

    Re: Carburetor 1001

    Post by duke on Sun Dec 06, 2009 1:08 pm

    meh cni aku try translate....

    Mikuni Motorcycle Carburetor Theory 101

    Karburetor motor nampak seakan rumit, tetapi dengan memahami sedikit teori, anda boleh tala motor untuk prestasi maksimum. Semua karburetor berfungsi menggunakan prinsip asas tekanan atmosfera. Tekanan atmosfera merupakan tenaga yang mengenakan tekanan terhadap semua benda. Nilainya berbeza-beza (e.g mengikut altitud) tetapi secara amnya dianggap sebagai 15 pound per seinci persegi - 15 pound per square inch (PSI). Ini bermakna tekanan atmosfera menekan semua benda pada kadar 15 PSI. Dengan mengubah tekanan atmosfera dalam enjin dan karburetor, kita mengubah tekanan dan membuat minyak & udara mengalir.

    Tekanan atmosfera akan memaksa tekanan tinggi kepada tekanan rendah. Sewaktu piston enjin dua stroke naik ke atas (atau turun ke bawah untuk enjin empat stroke), tekanan rendah akan terbentuk dalam crankcase (atau di atas piston dalam enjin empat stroke). Tekanan rendah ini juga akan menyebabkan tekanan rendah dalam karburetor. Memandangkan tekanan di luar enjin dan karburetor adalah lebih tinggi, udara akan ditolak masuk ke dalam karburetor dan enjin sehingga tekanan kembali sama rata. Udara yang melalui karburetor tadi akan bercampur dengan minyak.

    Dalam karburetor ada venturi, fig 1. Venturi ini merupakan liang kecil dalam karburetor yang memaksa udara bergerak lebih laju untuk melepasinya. Sebatang sungai yang semakin sempit boleh digunakan untuk menggambarkan apa yang berlaku dalam karburetor. Air sungai akan bergerak lebih pantas sewaktu menghampiri kawasan sempit ini dan lebih pantas lagi jika sungai menjadi lebih sempit. Perkara yang sama berlaku dalam karburetor. Udara yang semakin laju akan mengakibatkan penurunan tekanan udara di dalam karburetor. Lebih laju udara bergerak, lebih rendah tekanan di dalam karburetor.


    FIG 1

    to be continued...adoi penat gak translate nih

    duke

    Re: Carburetor 1001

    Post by duke on Sun Dec 06, 2009 6:18 pm

    Kebanyakan litar karburetor motor dikawal oleh kedudukan throttle dan bukan oleh putaran enjin. Terdapat lima "metering systems" utama dalam kebanyakan karburetor motor. Litar -litar "metering" ini bertindan antara satu sama lain dan merupakan:
    * pilot circuit
    * throttle valve
    * needle jet and jet needle
    * main jet
    * choke circuit

    Pilot circuit mempunyai dua bahagian yang boleh ditala, fig 2. Bahagian-bahagian itu ialah "pilot air screw" dan "pilot jet". Air screw terletak sama ada berhampiran sisi belakang karburetor atau pun berhampiran sisi hadapan. Jika ia terletak di sisi belakang, ia mengawal jumlah udara yang masuk ke litar. Jika ia diskru ke dalam, ia akan mengurangkan jumlah udara lalu memberi campuran minyak-udara yang "rich". Jika diskru ke luar, ini membolehkan lebih banyak udara mengalir masuk ke litar, mengakibatkan campuran yang "lean".

    Sebaliknya jika air screw terletak berhampiran sisi depan, ia mengawal minyak. Campuran adalah "lean" apabila diskru masuk dan "rich" jika diskru keluar. Sekiranya air screw perlu diputar lebih 2 pusingan untuk mendapat idle enjin yang terbaik, saiz "pilot jet" lebih kecil yang seterusnya akan diperlukan.


    FIG 2

    duke

    Re: Carburetor 1001

    Post by duke on Sun Dec 06, 2009 6:53 pm

    "Pilot jet" merupakan bahagian yang membekalkan kebanyakan daripada minyak semasa throttle dibuka sedikit. Terdapat lubang kecil di dalamnya yang menghadkan aliran minyak melaluinya. Kedua-dua "pilot air screw" dan "pilot jet" mempengaruhi fungsi karburetor dari tahap idle sehingga 1/4 bukaan throttle.

    "Slide valve" mengawal fungsi karburetor antara bukaan throttle 1/8 sehingga 1/2. Ia paling banyak mempengaruhi karburetor antara bukaan 1/8 sehingga 1/4 sahaja dan kurang mempengaruhi sehingga bukaan 1/2. Slide valve mempunyai pelbagai saiz dan saiznya ditentukan oleh berapa besar "cutaway" dari sisi belakangnya, fig 3. Lebih besar saiz cutaway, lebih "lean" campuran minyak-udara (kerana lebih banyak udara melaluinya) dan lebih kecil saiz cutaway akan menghasilkan campuran lebih "rich". "Valve" throttle mempunyai nombor tersendiri yang menerangkan saiz cutaway. Jika terdapat no. 3 pada slide, bermakna saiz cutaway 3.0mm, no. 1 adalah saiz 1.0mm (yang mana 1 lebih "rich" daripada 3).


    FIG 3

    "Jet needle" dan "needle jet" mempengaruhi fungsi karburetor daripada bukaan throttle 1/4 sehingga 3/4. Jet needle adalah rod panjang tirus yang mengawal berapa banyak minyak dibenarkan masuk ke dalam venturi. Lebih kecil rod, lebih "rich" campuran. Lebih tebal, maka campuran menjadi lebih "lean" kerana rod tebal tidak membenarkan jumlah kemasukan minyak ke dalam venturi sebanyak rod kecil. Rod-rod ini direka untuk memberi campuran minyak-udara yang berbeza-beza mengikut bukaan throttle. "Jet needle" mempunyai beberapa alur di atasnya. Klip akan masuk ke salah satu alur ini dan memegangnya agar tidak jatuh atau bergerak dari slide. Kedudukan klip boleh diubah untuk membuat enjin lebih "rich" ataupun "lean", fig 4. Sekiranya enjin perlu lebih "lean", klip akan dinaikkan ke atas. Ini akan membuatkan needle jatuh lebih dalam ke "needle jet" dan mengurangkan aliran minyak. Jika klip diturunkan, "jet needle" akan ditinggikan sedikit dan campuran akan menjadi lebih "rich".

    "Needle jet" adalah tempat di mana "jet needle" masuk. Bergantung kepada diameter dalaman "needle jet", ini akan mempengaruhi "jet needle". "Needle jet" dan "jet needle" berfungsi bersama bagi mengawal aliran minyak antara bukaan throttle 1/8 sehingga 3/4. Kebanyakan talaan pada julat bukaan ini dilakukan ke atas "jet needle", bukan "needle jet".


    FIG 4

    adoih sebu otak teman...sambung sok2 pulak la ye Sleep

    kurt2812

    Re: Carburetor 1001

    Post by kurt2812 on Mon Dec 07, 2009 5:38 am

    thanks a lot Bro Duke..huhuhu!! take your time..

    duke

    Re: Carburetor 1001

    Post by duke on Mon Dec 07, 2009 5:09 pm

    'Main jet' berfungsi untuk mengawal aliran minyak daripada bukaan throttle 3/4 sehingga habis, fig 5. Sebaik sahaja throttle dibuka secukupnya, 'jet needle' ditarik setinggi yang boleh daripada 'needle jet' dan saiz liang di 'main jet' mula mengawal aliran minyak. 'Main jet' mempunyai saiz liang yang berbeza-beza, lebih besar liang, lebih banyak minyak mengalir (dan lebih 'rich' lagi campuran udara-minyak). Lebih tinggi nombor pada 'main jet', lebih banyak minyak boleh mengalir melaluinya dan campuran akan menjadi lebih 'rich'.


    FIG 5

    Sistem choke digunakan untuk menghidupkan enjin sejuk. Memandangkan minyak di dalam enjin sejuk selalunya melekat ke dinding silinder disebabkan oleh kondensasi (condensation), campuran minyak-udara pada waktu berkenaan adalah terlalu 'lean' untuk menghidupkan enjin. Sistem choke akan menambah minyak kepada enjin untuk menggantikan minyak yang melekat pada dinding silinder tadi. Sebaik enjin mulai panas, kondensasi tidak lagi menjadi masalah, maka choke sudah tidak diperlukan.

    Campuran udara-minyak perlu berubah-ubah mengikut keperluan enjin. Nisbah ideal udara-minyak ialah 14.7 gram udara untuk setiap 1 gram minyak. Nisbah ideal ini hanya diperolehi bagi tempoh yang singkat semasa enjin berjalan. Disebabkan minyak tidak mengeluwap dengan lengkap pada halaju perlahan enjin atau semasa lebih banyak minyak digunakan pada halaju tinggi, nisbah sebenar udara-minyak semasa beroperasi selalunya lebih 'rich'. Fig 6 menunjukkan nisbah sebenar udara-minyak pada majoriti keadaan bukaan throttle.


    FIG 6

    pcq5913

    Re: Carburetor 1001

    Post by pcq5913 on Tue Dec 08, 2009 10:55 am

    TERIMA KASIH bro... baru la aku paham..... tapi aku pasti tak ramai yang paham bahasa omputih ni... bila ang alih bahasa dah tentu smua org paham maksud dia... What a Face Laughing Laughing cheers

    miruss87

    Re: Carburetor 1001

    Post by miruss87 on Fri Mar 05, 2010 5:00 pm

    bro apa beza carb krr150 ngn panther? adakah 2-2 dr kompeni yg sama KEIHIN?

    kipas

    Re: Carburetor 1001

    Post by kipas on Fri Mar 12, 2010 2:44 pm

    bro duke de bakat bleh jd translater nih...


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    duke

    Re: Carburetor 1001

    Post by duke on Fri Mar 12, 2010 3:43 pm

    kipas wrote:bro duke de bakat bleh jd translater nih...

    hehe ikut angin rajin tu datang, bole le
    ada lagi dua part x siap....x terbuat2 rabbit

    lennya12threh

    Re: Carburetor 1001

    Post by lennya12threh on Sat Aug 21, 2010 5:45 pm

    i have a question about the pilot air screw... on my carb i noticed the large idle screw that effects idle and also this other smaller screw which must be the pilot air screw...

    in the author's article he said the pilot air screw has different functions depending if it is at the front of back of the carb.. I am confused as you which side is the front and which is the back... My screw is closest to the side that goes to engine, on the opposite side of the fuel line entrance/filter and the side that goes to the air box. It is the closest to the front of the entire motorcycle, but considering the flow of air it is not on the entrance for air into the carb.. it is on the side that the air/fuel goes to the engine..

    so im not sure if it is on the front of back as mentioned by the author and not sure if turning it in or out will make it leaner.

    khor

    Re: Carburetor 1001

    Post by khor on Fri Feb 11, 2011 1:55 pm

    lennya12threh wrote:i have a question about the pilot air screw... on my carb i noticed the large idle screw that effects idle and also this other smaller screw which must be the pilot air screw...

    in the author's article he said the pilot air screw has different functions depending if it is at the front of back of the carb.. I am confused as you which side is the front and which is the back... My screw is closest to the side that goes to engine, on the opposite side of the fuel line entrance/filter and the side that goes to the air box. It is the closest to the front of the entire motorcycle, but considering the flow of air it is not on the entrance for air into the carb.. it is on the side that the air/fuel goes to the engine..

    so im not sure if it is on the front of back as mentioned by the author and not sure if turning it in or out will make it leaner.

    If the screw is at the Air box side then it is the air screw, if it's near the engine block side then it is for controlling the fuel. so in your case i think it is a pilot fuel screw.

    jayjeffrey

    Re: Carburetor 1001

    Post by jayjeffrey on Fri Feb 11, 2011 7:36 pm

    tightening(clockwise) air screw riches your fuel mixture vice-versa

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