JET?
Mar 11, 2004 | 12:59 PM
#1
Thread Starter
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Range Rover
Joined: Nov 2003
Posts: 141
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JET?
Ok i just bought a new 04 Z400. Had it out about 10 hrs now. Now i am ready to add something.What should i add? Can't spend alot of cash right now becuase i just spent alot on the bike. I see in the forms that people modify their Air box and re-jet to get more power. Seems pretty scheap to me. But does anyone have any detailed information on this? And i mean detailed. I am new to this so i could use any help. Any other cheap mods i can do?
Thanks,
Thanks,
Mar 11, 2004 | 01:43 PM
#2
Range Rover
Joined: Apr 2003
Posts: 177
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JET?
First change oil and replace the filter. The 04 stock pipe is improved over the 03.... For cheep mods you can remove the air box lid after changing the main from the stock 130 to about a 135~137.5 (Mikuni#) or #146 aftermarket jet. You will not have to change anything else at this point if you are near sea level.
Mar 11, 2004 | 11:37 PM
#5
Range Rover
Joined: Apr 2003
Posts: 177
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JET?
Originally posted by: rafiki47
You have that in an English Version. I did change the Oil and Filter. Now if i remove the Air box lif won't water get in there?
You have that in an English Version. I did change the Oil and Filter. Now if i remove the Air box lif won't water get in there?
Well if your a mudder... Leave all stock. It does well in the wet stuff. If you want more power you will have to loose the air box lid and find higher ground.
Mar 12, 2004 | 10:38 AM
#7
Pro Rider
Joined: Oct 2002
Posts: 660
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JET?
Overview: Jetting 101
Carburetor fuel circuits and functions:
1) Pilot jet/slow jet - Affects mixture from idle to 1/3 throttle opening. The pilot jet meters fuel to the "bottom end circuits"
2) Air screw - Meters air to pilot jet. It is usually located near the back or air box side of the carb. Turning in clockwise, will richen the pilot mixture. Turning out, counter clockwise, will lean out the pilot mixture. Average setting for most 2 strokes is 1 to 2 1/2 turns out. Refer to owner's manual.
Note: If the adjustment screw is in the front of the carb, it is a fuel screw and not an air screw; it is adjusted the opposite of the air screw. Most 4-strokes are this way.
3) Jet needle aka Needle - Affects the mixture from 1/4 throttle to full throttle. The needle is in the leanest position when the clip is on the top, and richest on the bottom. The needle calibrates the full to the change in throttle valve (slide) opening. The further down the needle is, the later the main jet comes on and the leaner the mixture at that point.
4) Main Jet - This circuit affects the mixture from 1/2 throttle to full throttle. This is your full blast top end circuit. This circuit is most accurately tuned by checking the plug for the correct color, sort of mocha brown.
5) Float/Float valve/Float level - Your owner's manual has the correct level and procedure for calibrating your bike. Here are some symptoms that would indicate the need for float adjustment.
A) If float level is too high, the float bowl overflows out the drain hoses, and fuel often blocks the air passages that allow the carb to de-pressurize. This causes a bog, or hiccup over large hits.
B) If float level is too low, the engine starves for fuel off idle, causing a "boooooowang" sound very similar to a pilot jet or air screw set too lean.
Jetting Guidelines; Eliminating the variables.
1) Never change more than one circuit at a time. You need this tool to tell you exactly which circuit is affecting performance and at what throttle opening.
2) Use fresh gas. Octane ratings diminish with time and the higher the octane the slower the burn and richer the mixture. The quality of today’s pump gas is decreasing. To compensate for the fuel, richer jets are required. Also note that fuel with ethanol (aka MTBE) also requires a slightly richer mixture.
3) Always start with a fresh air filter. Let a freshly oiled air filter dry at least 6 hours in advance so that the alcohol in the air filter can evaporate. Then match the carb to a motor that breathes properly. Otherwise, the engine will run slightly leaner when the clean air filter is installed.
4) When performing a plug check, use a good used spark plug. New plugs are white and are hard to read accurately for mixture checks. If you have to use a new plug be sure to put at least 15 to 20 hard minutes on it before attempting to get a reading.
5) Always check for clogged carb vent lines. Clogged lines will cause hard starting and bogging when the motor is hot. They can also cause erratic running that seems to mimic a mis-adjusted float, but worse. Performance will seem rich and acceleration will be sluggish off idle.
6) If you’re trying to track down a jetting problem, don’t change your premix oil brand or the ratio. The pre-mix ratio will determine how much fuel is available to be burned because the oil isn’t burned, and in terms of liquid volume, the oil takes up a portion of the liquid (oil + fuel). While the ratio will have a minimal impact when making small changes, remember that you’re trying to eliminate variables.
How to Jet
1) Mark your throttle housing and grip in 1/4 turn increments. Use a marker, razor blade, etc.
2) Now get the motor to operating temperature by riding around, away from the pits.
3) Once the motor is warm, ride in 2nd and 3rd gear from the low RPM to high RPM. This puts a good load on the motor and is an accurate test of performance.
* try to notice if the problem gets worse or better as the motor heats up.
4) Now try to locate the throttle opening at which the problem exists. See details just below.
Rich Jetting Symptoms and Solutions
A) Motor won’t idle and idle set screw is ineffective. Try leaning out the air screw by turning it counter clockwise a quarter turn at a time. If the air screw has no effect, install a leaner pilot jet and return the air screw to 1 turn out. Proper air screw settings are usually between 1 and 2 1/2 turns out. The correct pilot for your bike is one that allows instant off-idle throttle response, and allows the air screw to be effective between 1 and 2.5 turns out. If the problem still exists, check and clean the choke circuit and carb vent lines.
B) Motor stumbles off idle to 1/2 throttle, then cleans up. If everything in part A above is correct, check the needle. Stock position is usually in the middle, but check your owner’s manual to be sure. To lean out the needle, you need to raise the clip. If the needle is dropped all the way lean and problem still exists, try a leaner needle.
C. Motor will rev through the mid range then becomes gurgley (technical term) at full throttle and power is sluggish. This is a text book example of a rich main jet. This problem often occurs when an air filter becomes clogged and gets worse as the motor heats up. Choose a main jet with a smaller number and lean out the air fuel mixture one step at a time. If the problem still persists even though it’s improved a little, reinstall your original main jet and lean out the needle one position. Now fine tune the main jet with plug checks.
Plug checks are the key to fine tuning the main jet once the other circuits are set.
White Porcelain Chocolate Mocha Brown Black/Wet
Lean Perfect! Rich
Look for symmetrical burn patterns, smell for odors like burnt plastic, which is actually tranny fluid and would be indicative of a blown seal.
Lean Jetting Symptoms and Solutions
A) Motor hesitates off idle with a "Boooooooooowang" sound. This is a lean symptom and often occurs when a motor is cold. Try turning the air-fuel screw clockwise a quarter turn richer and check throttle response again until motor revs without hesitation. If the motor "hangs up" or doesn’t come right back down to idle, install a richer pilot, and reset air screw.
B) Motor knock knock knocks at idle when hot. Try solution A. If problem persists, perform a "leakdown pressure test" to check for ignition crank seal leakage.
C) Motor revs clean and crisp but runs really hot and lacks power. This symptom indicates a lean main jet and/or needle. Use a richer main jet and/or needle setting. This is the most common misconception about two stroke jetting: When a motor runs excessively hot and lacks power, it is on the verge of seizing. If you are on the trail and don’t have the right main jet, try raising the needle by lowering the clip. It won’t be exact but at least you won’t seize.
Note: To be certain that your problem is lean, pull on the choke and see if the problem gets better or worse. If better, your problem is a lean condition.
These jetting tips are provided courtesty of Alex Dicharry from DNA Racing.
Carburetor fuel circuits and functions:
1) Pilot jet/slow jet - Affects mixture from idle to 1/3 throttle opening. The pilot jet meters fuel to the "bottom end circuits"
2) Air screw - Meters air to pilot jet. It is usually located near the back or air box side of the carb. Turning in clockwise, will richen the pilot mixture. Turning out, counter clockwise, will lean out the pilot mixture. Average setting for most 2 strokes is 1 to 2 1/2 turns out. Refer to owner's manual.
Note: If the adjustment screw is in the front of the carb, it is a fuel screw and not an air screw; it is adjusted the opposite of the air screw. Most 4-strokes are this way.
3) Jet needle aka Needle - Affects the mixture from 1/4 throttle to full throttle. The needle is in the leanest position when the clip is on the top, and richest on the bottom. The needle calibrates the full to the change in throttle valve (slide) opening. The further down the needle is, the later the main jet comes on and the leaner the mixture at that point.
4) Main Jet - This circuit affects the mixture from 1/2 throttle to full throttle. This is your full blast top end circuit. This circuit is most accurately tuned by checking the plug for the correct color, sort of mocha brown.
5) Float/Float valve/Float level - Your owner's manual has the correct level and procedure for calibrating your bike. Here are some symptoms that would indicate the need for float adjustment.
A) If float level is too high, the float bowl overflows out the drain hoses, and fuel often blocks the air passages that allow the carb to de-pressurize. This causes a bog, or hiccup over large hits.
B) If float level is too low, the engine starves for fuel off idle, causing a "boooooowang" sound very similar to a pilot jet or air screw set too lean.
Jetting Guidelines; Eliminating the variables.
1) Never change more than one circuit at a time. You need this tool to tell you exactly which circuit is affecting performance and at what throttle opening.
2) Use fresh gas. Octane ratings diminish with time and the higher the octane the slower the burn and richer the mixture. The quality of today’s pump gas is decreasing. To compensate for the fuel, richer jets are required. Also note that fuel with ethanol (aka MTBE) also requires a slightly richer mixture.
3) Always start with a fresh air filter. Let a freshly oiled air filter dry at least 6 hours in advance so that the alcohol in the air filter can evaporate. Then match the carb to a motor that breathes properly. Otherwise, the engine will run slightly leaner when the clean air filter is installed.
4) When performing a plug check, use a good used spark plug. New plugs are white and are hard to read accurately for mixture checks. If you have to use a new plug be sure to put at least 15 to 20 hard minutes on it before attempting to get a reading.
5) Always check for clogged carb vent lines. Clogged lines will cause hard starting and bogging when the motor is hot. They can also cause erratic running that seems to mimic a mis-adjusted float, but worse. Performance will seem rich and acceleration will be sluggish off idle.
6) If you’re trying to track down a jetting problem, don’t change your premix oil brand or the ratio. The pre-mix ratio will determine how much fuel is available to be burned because the oil isn’t burned, and in terms of liquid volume, the oil takes up a portion of the liquid (oil + fuel). While the ratio will have a minimal impact when making small changes, remember that you’re trying to eliminate variables.
How to Jet
1) Mark your throttle housing and grip in 1/4 turn increments. Use a marker, razor blade, etc.
2) Now get the motor to operating temperature by riding around, away from the pits.
3) Once the motor is warm, ride in 2nd and 3rd gear from the low RPM to high RPM. This puts a good load on the motor and is an accurate test of performance.
* try to notice if the problem gets worse or better as the motor heats up.
4) Now try to locate the throttle opening at which the problem exists. See details just below.
Rich Jetting Symptoms and Solutions
A) Motor won’t idle and idle set screw is ineffective. Try leaning out the air screw by turning it counter clockwise a quarter turn at a time. If the air screw has no effect, install a leaner pilot jet and return the air screw to 1 turn out. Proper air screw settings are usually between 1 and 2 1/2 turns out. The correct pilot for your bike is one that allows instant off-idle throttle response, and allows the air screw to be effective between 1 and 2.5 turns out. If the problem still exists, check and clean the choke circuit and carb vent lines.
B) Motor stumbles off idle to 1/2 throttle, then cleans up. If everything in part A above is correct, check the needle. Stock position is usually in the middle, but check your owner’s manual to be sure. To lean out the needle, you need to raise the clip. If the needle is dropped all the way lean and problem still exists, try a leaner needle.
C. Motor will rev through the mid range then becomes gurgley (technical term) at full throttle and power is sluggish. This is a text book example of a rich main jet. This problem often occurs when an air filter becomes clogged and gets worse as the motor heats up. Choose a main jet with a smaller number and lean out the air fuel mixture one step at a time. If the problem still persists even though it’s improved a little, reinstall your original main jet and lean out the needle one position. Now fine tune the main jet with plug checks.
Plug checks are the key to fine tuning the main jet once the other circuits are set.
White Porcelain Chocolate Mocha Brown Black/Wet
Lean Perfect! Rich
Look for symmetrical burn patterns, smell for odors like burnt plastic, which is actually tranny fluid and would be indicative of a blown seal.
Lean Jetting Symptoms and Solutions
A) Motor hesitates off idle with a "Boooooooooowang" sound. This is a lean symptom and often occurs when a motor is cold. Try turning the air-fuel screw clockwise a quarter turn richer and check throttle response again until motor revs without hesitation. If the motor "hangs up" or doesn’t come right back down to idle, install a richer pilot, and reset air screw.
B) Motor knock knock knocks at idle when hot. Try solution A. If problem persists, perform a "leakdown pressure test" to check for ignition crank seal leakage.
C) Motor revs clean and crisp but runs really hot and lacks power. This symptom indicates a lean main jet and/or needle. Use a richer main jet and/or needle setting. This is the most common misconception about two stroke jetting: When a motor runs excessively hot and lacks power, it is on the verge of seizing. If you are on the trail and don’t have the right main jet, try raising the needle by lowering the clip. It won’t be exact but at least you won’t seize.
Note: To be certain that your problem is lean, pull on the choke and see if the problem gets better or worse. If better, your problem is a lean condition.
These jetting tips are provided courtesty of Alex Dicharry from DNA Racing.
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Mar 12, 2004 | 10:54 AM
#8
Pro Rider
Joined: Oct 2002
Posts: 660
Likes: 0
JET?
Jetting
The following is how Bill ARF would explain to someone how to change the Main Jet on a Z400 or KFX400.
About the right jet size ....you will have to experiment to find out what's best for your bike. The following will prove helpful when you do your rejetting..
The actual change of the Main Jet is easy, except the first time and the getting the float bowl screws out so you can get to the jets is a headache! Read on...
Your first rejetting experience on a Z400 /KFX400 may be a major headache! Getting off the float bowl screws can be a major problem the first time you do it. I had to use a needle nose vice grip plier (NEEDLE NOSE VICE GRIP) to grab the screw heads and loosen the screws. (Some people say an "impact screwdriver will do the job of getting the screws loose) The stock phillips slots quit even though I used a new, properly sized phillips head driver with lots of pressure. The last screw was so tight I could not even budge it with the vice grips so I drilled the head of it off and then it came out easily. (Also a dremel could could possibly have been used to place a cut in that screw that a flat-tip screwdriver would work with).
I replaced the stock screws with plain steel cap screw socket (allen head) screws "4mm x 10mm "purchased at Home Depot". Even better would have been stainless steel screws. Be sure not to go longer then 10mm or risk damage to carb. Use plenty of anti-seize and be sure to work the screws in and out so the anti-seize coats all well. Anyway, jet change was easy BUT nightmare this first time because of soft metal stock bowl screws. I might mention Kawasaki uses those screws as other metal screws will react with the aluminum and kind of weld themselves. MUST use anti-seize on replacement regular steel screws or risk problems.
Look below at the pic of the carb. The pic is labeled. The main jet is the the one that looks like it is sitting in a brass/gold colored bowl. You remove that main jet with a flat tip screwdriver and replace it.. easy to do. By the way, did not remove the carb to do the jet change. Loosened clamps and turned the carb. Had to unbolt temporarily the small black box that resides on the other side of the carb. Once the carb is turned toward you a bit you can easily get to the float bowl screws. Again, they are a pain to get off. After changing the main jet reverse the above procedure.. turn the carb back in position, retighten clamps. Note, if you can't get to the float bowl screws to do what you need to do to get them off, slip the carb out of the rubber carb boot and lower it an inch or 2 and turn it toward you til you can get to it. Gently, don't pull, force, etc.. Go easy turning it, pulling on it as it has cables going into the top of it, etc.. SO, that is pretty much it. Quite easy to do except for the float bowl screws as I and others have said. IF you are not familar with tools you might want to get someone who is to help you get the float bowl screws out. Be sure to go to Lowes or Home Depot, etc. and get new allen head screws as described above before you start the jet change procedure!
About buying/obtaining correct jet:
When you go to your local stealership to buy main jets for my Z400 / KFX400 they may try to sell you the squatty LARGER DIAMETER round Mikuni versus the Mikuni that is a SMALL diameter on top and round shape. The parts counter guy may say ... "ah, it should work". Anyway, go with the smaller round shaped one and not the larger diameter round and squatty one. Part numbers for the correct/right genuine Mikuni "MAIN" JETS all start with: N102/221 and then the jet size. So when you buy/order genuine Mikuni jets at your Kawi or Suki dealer you will see the manufacturers part # (Mikuni's part #) numbers for the main jet you need/want that look like this on your receipt:
N102/221-130 (Stock Main Jet)
N102/221-150
N102/221-160
N102/221-165
N102/221-167.5
N102/221-170
These are just examples of the manufacturers (Mikuni) part numbers and not all the available Main Jet SIZES available from Mikuni for your bike.
- Jet sizes are stamped on each jet. -
Written by BillArf
The following is how Bill ARF would explain to someone how to change the Main Jet on a Z400 or KFX400.
About the right jet size ....you will have to experiment to find out what's best for your bike. The following will prove helpful when you do your rejetting..
The actual change of the Main Jet is easy, except the first time and the getting the float bowl screws out so you can get to the jets is a headache! Read on...
Your first rejetting experience on a Z400 /KFX400 may be a major headache! Getting off the float bowl screws can be a major problem the first time you do it. I had to use a needle nose vice grip plier (NEEDLE NOSE VICE GRIP) to grab the screw heads and loosen the screws. (Some people say an "impact screwdriver will do the job of getting the screws loose) The stock phillips slots quit even though I used a new, properly sized phillips head driver with lots of pressure. The last screw was so tight I could not even budge it with the vice grips so I drilled the head of it off and then it came out easily. (Also a dremel could could possibly have been used to place a cut in that screw that a flat-tip screwdriver would work with).
I replaced the stock screws with plain steel cap screw socket (allen head) screws "4mm x 10mm "purchased at Home Depot". Even better would have been stainless steel screws. Be sure not to go longer then 10mm or risk damage to carb. Use plenty of anti-seize and be sure to work the screws in and out so the anti-seize coats all well. Anyway, jet change was easy BUT nightmare this first time because of soft metal stock bowl screws. I might mention Kawasaki uses those screws as other metal screws will react with the aluminum and kind of weld themselves. MUST use anti-seize on replacement regular steel screws or risk problems.
Look below at the pic of the carb. The pic is labeled. The main jet is the the one that looks like it is sitting in a brass/gold colored bowl. You remove that main jet with a flat tip screwdriver and replace it.. easy to do. By the way, did not remove the carb to do the jet change. Loosened clamps and turned the carb. Had to unbolt temporarily the small black box that resides on the other side of the carb. Once the carb is turned toward you a bit you can easily get to the float bowl screws. Again, they are a pain to get off. After changing the main jet reverse the above procedure.. turn the carb back in position, retighten clamps. Note, if you can't get to the float bowl screws to do what you need to do to get them off, slip the carb out of the rubber carb boot and lower it an inch or 2 and turn it toward you til you can get to it. Gently, don't pull, force, etc.. Go easy turning it, pulling on it as it has cables going into the top of it, etc.. SO, that is pretty much it. Quite easy to do except for the float bowl screws as I and others have said. IF you are not familar with tools you might want to get someone who is to help you get the float bowl screws out. Be sure to go to Lowes or Home Depot, etc. and get new allen head screws as described above before you start the jet change procedure!
About buying/obtaining correct jet:
When you go to your local stealership to buy main jets for my Z400 / KFX400 they may try to sell you the squatty LARGER DIAMETER round Mikuni versus the Mikuni that is a SMALL diameter on top and round shape. The parts counter guy may say ... "ah, it should work". Anyway, go with the smaller round shaped one and not the larger diameter round and squatty one. Part numbers for the correct/right genuine Mikuni "MAIN" JETS all start with: N102/221 and then the jet size. So when you buy/order genuine Mikuni jets at your Kawi or Suki dealer you will see the manufacturers part # (Mikuni's part #) numbers for the main jet you need/want that look like this on your receipt:
N102/221-130 (Stock Main Jet)
N102/221-150
N102/221-160
N102/221-165
N102/221-167.5
N102/221-170
These are just examples of the manufacturers (Mikuni) part numbers and not all the available Main Jet SIZES available from Mikuni for your bike.
- Jet sizes are stamped on each jet. -
Written by BillArf
