Spankeys Jetting Guide - Info 2 Stroke riders must have

Firestorm · 12-27-2005

Spanky's Jetting Guide:

A correctly jetted carb makes a tremendous difference in the torque, midrange pull, top-end pull, and over-rev of your engine. If you have never jetted your bike correctly, you will almost certainly gain some performance at some point in the bike's powerband.

A cleanly jetted pilot circuit can be the difference between having to clutch the bike out of a turn or not. The needle can make all the difference in the world for the power of the machine in most situations, as it controls the throttle range that most riders spend most of their time using.

A correctly sized main jet could mean the difference between being able to rev out high enough to not have to shift one more time at the end of the straight, or the power falling flat on top and requiring you to make that extra shift.

Are you fouling plugs? Many people will tell you all sorts of band-aid fixes, from running less oil, to running a hotter plug. Both are incorrect fixes for plug fouling. It's all in the jetting.

The only way to know what jetting changes you will need is by trial-and-error. No one can give you jetting specs, because every bike is different, every rider has a different style, and jetting is totally weather dependent. Unless the person telling you what jets to use is riding an identical bike, on the exact same track, at the same time, his recommendations are meaningless.

Jetting is fairly simple, and is a useful skill to learn if you ride a two-stroke and want it to perform at it's best.

It's very important that you start with the pilot circuit. The reason is simple. The pilot circuit affects the entire throttle range. When you are at full throttle, the main jet is the primary fuel metering device, but the pilot is still delivering fuel as well, adding to the total amount of fuel that your engine is receiving.

Before you start to rejet your bike, you need a clean air filter, a fresh plug (actually you need several plugs to do plug-chop tests for the main jet), and fresh fuel.

One important detail: Make sure the engine is in good mechanical condition. If your engine has a worn top-end, fix it first. Trying to jet a worn out engine is a waste of time. The same goes for reeds that don't seal properly, and a silencer that needs re-packing. Worn reeds will mimic rich jetting, and worn rings will mimic lean jetting.

Before you start the jet testing, Install a fresh plug. Set the float level to the proper specs, an incorrect float height will affect your jetting all across the throttle range.

Warm the bike completely, and shut it off.

As already stated, start with the pilot circuit. Turn the air screw all the way in, then turn it out 1.5 turns to start. Start the engine, and turn the idle screw in until you get a slightly fast idle, or hold the throttle just barely cracked, to keep the engine idleing. Turn the airscrew slowly in, and then out, until you find the point where the idle is fastest. Stop there. Do not open the screw any farther, or your throttle response will be flat and mushy, and the bike may even bog. This is only the starting point, we will still have to tune the air screw for the best response.

Now is the time to determine if you have the correct pilot installed in your carb. The air screw position determines this for you, making it very simple. If your air screw is less than 1 turn from closed, you need a larger pilot jet. If it is more than 2.5 turns from closed, you need a smaller pilot jet.

Once you have determined (and installed it if it's neccessary to change it) the correct pilot jet size, and tuned the air screw for the fastest idle, it's time to tune the air screw for the best throttle response. Again, make sure the bike is at full operating temperature. Set the idle back down (the bike should still idle, despite what you read in the Moto Tabloids), and ride the bike, using closed-to-1/4 throttle transitions. Turn the air screw slightly in either direction until you find the point that gives you the best response when cracking the throttle open. Most bikes are sensitive to changes as small as 1/8 of a turn.

The air screw is not a set-it-and-leave-it adjustment. You have to constantly re-adjust the air screw to compensate for changing outdoor temps and humidity. An air screw setting that is perfect in the cool morning air will likely be too rich in the heat of the mid-day.

Now, it's time to work on the needle. Mark the throttle grip at 1/4 and 3/4 openings. Ride the bike between these two marks. If the bike bogs for a second before responding to throttle, lower the clip (raising the needle) a notch at a time until the engine picks up smoothly. If the bike sputters or sounds rough when giving it throttle, raise the clip (lowering the needle) until it runs cleanly. There isn't really any way to test the needle other than by feel, but it's usually quite obvious when it's right or wrong.

Last is the main jet. The main jet affects from 1/2 to full throttle. The easiest way to test it is to do a throttle-chop test. With the bike fully warmed up, find a long straight, and install a fresh plug. Start the engine, and do a full-throttle run down the straight, through all gears. As soon as the bike tops out, pull the clutch in, and kill the engine, coasting to a stop. Remove the plug, and look deep down inside the threads, at the base of the insulator. If it is white or gray, the main is too lean. If it is dark brown or black, the main is too rich. The correct color is a medium-dark mocha brown or tan.

Once you have a little bit of experience with jetting changes, and you start to learn the difference in feel between "rich" and "lean", you'll begine to learn, just from the sound of the exhaust and the feel of the power, not only if the bike is running rich or lean, but even which one of the carb circuits is the culprit.

The slide is also a tuning variable for jetting, but slides are very expensive, and few bikes need different slides, so we won't go into that here.

Keep in mind, even though this article is intended primarily for two-strokes, four-strokes also need proper jetting to perform right, although they are not quite as fussy as their oil-burning cousins. The only real difference in the two is with the pilot circuit.

Two-strokes have an air screw that you screw in to make the jetting richer, ansd screw out to make the jetting leaner. Four-strokes, on the other hand, have a fuel adjustment screw that you screw in to make the jetting leaner, and out to make it richer.

iracekx · 10-09-2007

This guide is awesome thanks!

acomputerdude · 10-10-2007

Thanks, I needed that!

KickassKX125 · 02-11-2008

+1, Bump to the top of the forum to help some more people before it dies

jandb917 · 02-11-2008

i think this need to be a sticky note ..... I mean come on how many people need help with jetting on here.... i mean i have no promblem with helping but you have to help yourself first lol

stevied645 · 02-12-2008

+1 I agree think there is at least 1 question a day about jetting lol

KickassKX125 · 02-12-2008

+2 How do we get it Stickified?

stevied645 · 02-13-2008

Can we have this stickied please.

KickassKX125 · 02-13-2008

I sent Tod a PM asking him to sticky it.

*Tod* · 02-13-2008

Tis good info. Consider it stuck.

stevied645 · 02-13-2008

thank you

KickassKX125 · 02-13-2008

NATE HEAD MIAMI · 05-13-2008

This Is Some Good Advice Im Goin To Try This Right Now On My Kx 85 Lol I Also Saved It Myself So I Can Use It Outside While I Fix My Jetting So I Do Not Make Any Mistakes Thanks You Know Alot About These Machines

MoToMaStR · 05-20-2008

Right on man, thanks!! I was going nuts trying to figure out why my bike started to run like dog-sh*t and stall as it got warmer and more humid here in southwest florida. I swapped my 160 to a 158 and my 52 to a 48. running 32:1 full synthetic redline racing 2cycle mix and 94 oct pump gas. my baby runs great now in dump water FL swamp land. I cant wait to drag it back out to so-cal and tear up glamis and imperial dezzurt again. FL SUCKS!

snh1968 · 07-12-2008

Could someone give me the web address for Team Green specs? Thanks

winkbynight · 07-15-2008

hi guys i got a kx 80 and its slow at hiting the power band but when i put the chok on it fast but then it seams like if its geting to much petrul i fink the mixer scerw needs setting dus any 1 no the settings and i tuk the plug out and its black can any 1 help me thks guys

josh l.93 · 08-11-2008

^^^

ime exactly the same.. i dont know the stock carb settings for my kx100

josh l.93 · 08-11-2008

ive followed the guide.. but my bike jus wont idle.. no matter what.. and then it stopped hittin powerband... and now wont even start

rahulmittal · 10-10-2008

I think this need to be a sticky note. I mean how many people need help with jetting on here. I mean I have no problem with helping but you have to help yourself first.
__________________________________________________ _________________________
Rahul

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Fatcat 1 · 10-10-2008

Quote:

Originally Posted by rahulmittal

I think this need to be a sticky note. I mean how many people need help with jetting on here. I mean I have no problem with helping but you have to help yourself first.
__________________________________________________ _________________________
Rahul

Houston Best Florist loans with no credit check pisos vilafranca download iPhone ringtones

uhh it is!

12-27-2005	#1 (permalink)
Firestorm Vampire BTK Expert Join Date: Apr 2005 Location: Scotland, UK Posts: 761	Spankeys Jetting Guide - Info 2 Stroke riders must have Spanky's Jetting Guide: A correctly jetted carb makes a tremendous difference in the torque, midrange pull, top-end pull, and over-rev of your engine. If you have never jetted your bike correctly, you will almost certainly gain some performance at some point in the bike's powerband. A cleanly jetted pilot circuit can be the difference between having to clutch the bike out of a turn or not. The needle can make all the difference in the world for the power of the machine in most situations, as it controls the throttle range that most riders spend most of their time using. A correctly sized main jet could mean the difference between being able to rev out high enough to not have to shift one more time at the end of the straight, or the power falling flat on top and requiring you to make that extra shift. Are you fouling plugs? Many people will tell you all sorts of band-aid fixes, from running less oil, to running a hotter plug. Both are incorrect fixes for plug fouling. It's all in the jetting. The only way to know what jetting changes you will need is by trial-and-error. No one can give you jetting specs, because every bike is different, every rider has a different style, and jetting is totally weather dependent. Unless the person telling you what jets to use is riding an identical bike, on the exact same track, at the same time, his recommendations are meaningless. Jetting is fairly simple, and is a useful skill to learn if you ride a two-stroke and want it to perform at it's best. It's very important that you start with the pilot circuit. The reason is simple. The pilot circuit affects the entire throttle range. When you are at full throttle, the main jet is the primary fuel metering device, but the pilot is still delivering fuel as well, adding to the total amount of fuel that your engine is receiving. Before you start to rejet your bike, you need a clean air filter, a fresh plug (actually you need several plugs to do plug-chop tests for the main jet), and fresh fuel. One important detail: Make sure the engine is in good mechanical condition. If your engine has a worn top-end, fix it first. Trying to jet a worn out engine is a waste of time. The same goes for reeds that don't seal properly, and a silencer that needs re-packing. Worn reeds will mimic rich jetting, and worn rings will mimic lean jetting. Before you start the jet testing, Install a fresh plug. Set the float level to the proper specs, an incorrect float height will affect your jetting all across the throttle range. Warm the bike completely, and shut it off. As already stated, start with the pilot circuit. Turn the air screw all the way in, then turn it out 1.5 turns to start. Start the engine, and turn the idle screw in until you get a slightly fast idle, or hold the throttle just barely cracked, to keep the engine idleing. Turn the airscrew slowly in, and then out, until you find the point where the idle is fastest. Stop there. Do not open the screw any farther, or your throttle response will be flat and mushy, and the bike may even bog. This is only the starting point, we will still have to tune the air screw for the best response. Now is the time to determine if you have the correct pilot installed in your carb. The air screw position determines this for you, making it very simple. If your air screw is less than 1 turn from closed, you need a larger pilot jet. If it is more than 2.5 turns from closed, you need a smaller pilot jet. Once you have determined (and installed it if it's neccessary to change it) the correct pilot jet size, and tuned the air screw for the fastest idle, it's time to tune the air screw for the best throttle response. Again, make sure the bike is at full operating temperature. Set the idle back down (the bike should still idle, despite what you read in the Moto Tabloids), and ride the bike, using closed-to-1/4 throttle transitions. Turn the air screw slightly in either direction until you find the point that gives you the best response when cracking the throttle open. Most bikes are sensitive to changes as small as 1/8 of a turn. The air screw is not a set-it-and-leave-it adjustment. You have to constantly re-adjust the air screw to compensate for changing outdoor temps and humidity. An air screw setting that is perfect in the cool morning air will likely be too rich in the heat of the mid-day. Now, it's time to work on the needle. Mark the throttle grip at 1/4 and 3/4 openings. Ride the bike between these two marks. If the bike bogs for a second before responding to throttle, lower the clip (raising the needle) a notch at a time until the engine picks up smoothly. If the bike sputters or sounds rough when giving it throttle, raise the clip (lowering the needle) until it runs cleanly. There isn't really any way to test the needle other than by feel, but it's usually quite obvious when it's right or wrong. Last is the main jet. The main jet affects from 1/2 to full throttle. The easiest way to test it is to do a throttle-chop test. With the bike fully warmed up, find a long straight, and install a fresh plug. Start the engine, and do a full-throttle run down the straight, through all gears. As soon as the bike tops out, pull the clutch in, and kill the engine, coasting to a stop. Remove the plug, and look deep down inside the threads, at the base of the insulator. If it is white or gray, the main is too lean. If it is dark brown or black, the main is too rich. The correct color is a medium-dark mocha brown or tan. Once you have a little bit of experience with jetting changes, and you start to learn the difference in feel between "rich" and "lean", you'll begine to learn, just from the sound of the exhaust and the feel of the power, not only if the bike is running rich or lean, but even which one of the carb circuits is the culprit. The slide is also a tuning variable for jetting, but slides are very expensive, and few bikes need different slides, so we won't go into that here. Keep in mind, even though this article is intended primarily for two-strokes, four-strokes also need proper jetting to perform right, although they are not quite as fussy as their oil-burning cousins. The only real difference in the two is with the pilot circuit. Two-strokes have an air screw that you screw in to make the jetting richer, ansd screw out to make the jetting leaner. Four-strokes, on the other hand, have a fuel adjustment screw that you screw in to make the jetting leaner, and out to make it richer. __________________ -Ace '06 CBR125RS - SOLD '90 VFR400 http://graphicalsource.ipbfree.com

10-09-2007	#2 (permalink)
iracekx Real Men Ride Rockets BTK Intermediate Join Date: Nov 2006 Location: Waxahachie, TX Posts: 195	This guide is awesome thanks! __________________ Life begins @ 150.....on a 2005 Blue R1!!!!!!

10-10-2007	#3 (permalink)
acomputerdude Newbie Join Date: Apr 2007 Posts: 14	Thanks, I needed that! __________________ Visit Our Website at MxResultz.com

02-11-2008	#4 (permalink)
KickassKX125 Now after another 125!! BTK Expert Join Date: May 2007 Location: Helmsley, North Yorkshire, England, UK Posts: 888	+1, Bump to the top of the forum to help some more people before it dies __________________ Jamie Bought 1996 CR250 but need to pick up. Now after another Mad Kaw 125 to tear the garden up!

02-11-2008	#5 (permalink)
jandb917 pre mix for blood BTK Intermediate Join Date: Jul 2007 Location: kansas Posts: 150	i think this need to be a sticky note ..... I mean come on how many people need help with jetting on here.... i mean i have no promblem with helping but you have to help yourself first lol __________________ You better watch out ....." IM COMMIN AT YOU LIKE A SPIDER MONKEY "

02-12-2008	#6 (permalink)
stevied645 Wants better weather! BTK Expert Join Date: Nov 2007 Location: Scotland Posts: 728	+1 I agree think there is at least 1 question a day about jetting lol __________________ *KX250/500 Hybrid LOL Scary Stuff*

02-12-2008	#7 (permalink)
KickassKX125 Now after another 125!! BTK Expert Join Date: May 2007 Location: Helmsley, North Yorkshire, England, UK Posts: 888	+2 How do we get it Stickified? __________________ Jamie Bought 1996 CR250 but need to pick up. Now after another Mad Kaw 125 to tear the garden up!

02-13-2008	#8 (permalink)
stevied645 Wants better weather! BTK Expert Join Date: Nov 2007 Location: Scotland Posts: 728	Can we have this stickied please. __________________ *KX250/500 Hybrid LOL Scary Stuff*

02-13-2008	#9 (permalink)
KickassKX125 Now after another 125!! BTK Expert Join Date: May 2007 Location: Helmsley, North Yorkshire, England, UK Posts: 888	I sent Tod a PM asking him to sticky it. __________________ Jamie Bought 1996 CR250 but need to pick up. Now after another Mad Kaw 125 to tear the garden up!

02-13-2008	#10 (permalink)
Tod Speed Learner Extreme Forum Supporter Join Date: Aug 2005 Location: Round Rock, TX Posts: 19,861	Tis good info. Consider it stuck. __________________ “Laughing at our mistakes can lengthen our own life. Laughing at someone else's can shorten it.” - Cullen Hightower

02-13-2008	#11 (permalink)
stevied645 Wants better weather! BTK Expert Join Date: Nov 2007 Location: Scotland Posts: 728	thank you __________________ *KX250/500 Hybrid LOL Scary Stuff*

02-13-2008	#12 (permalink)
KickassKX125 Now after another 125!! BTK Expert Join Date: May 2007 Location: Helmsley, North Yorkshire, England, UK Posts: 888	Ta. __________________ Jamie Bought 1996 CR250 but need to pick up. Now after another Mad Kaw 125 to tear the garden up! Last edited by KickassKX125 : 03-28-2008 at 09:51 AM.

05-13-2008	#13 (permalink)
NATE HEAD MIAMI Still On The Kickstand BTK Beginner Join Date: May 2008 Location: MIAMI FLORIDA Posts: 41	This Is Some Good Advice Im Goin To Try This Right Now On My Kx 85 Lol I Also Saved It Myself So I Can Use It Outside While I Fix My Jetting So I Do Not Make Any Mistakes Thanks You Know Alot About These Machines __________________ MIAMI RIDER

05-20-2008	#14 (permalink)
MoToMaStR The Welder Join Date: May 2008 Location: FL till june, then back to diego! Posts: 36	Right on man, thanks!! I was going nuts trying to figure out why my bike started to run like dog-sh*t and stall as it got warmer and more humid here in southwest florida. I swapped my 160 to a 158 and my 52 to a 48. running 32:1 full synthetic redline racing 2cycle mix and 94 oct pump gas. my baby runs great now in dump water FL swamp land. I cant wait to drag it back out to so-cal and tear up glamis and imperial dezzurt again. FL SUCKS!

07-12-2008	#15 (permalink)
snh1968 Newbie Join Date: Jun 2008 Posts: 1	Could someone give me the web address for Team Green specs? Thanks

07-15-2008	#16 (permalink)
winkbynight Newbie Join Date: Jun 2008 Location: birmingham Posts: 11	hi guys i got a kx 80 and its slow at hiting the power band but when i put the chok on it fast but then it seams like if its geting to much petrul i fink the mixer scerw needs setting dus any 1 no the settings and i tuk the plug out and its black can any 1 help me thks guys

08-11-2008	#17 (permalink)
josh l.93 Newbie Join Date: Aug 2008 Posts: 8	^^^ ime exactly the same.. i dont know the stock carb settings for my kx100

08-11-2008	#18 (permalink)
josh l.93 Newbie Join Date: Aug 2008 Posts: 8	ive followed the guide.. but my bike jus wont idle.. no matter what.. and then it stopped hittin powerband... and now wont even start

10-10-2008	#19 (permalink)
rahulmittal Banned Join Date: Oct 2008 Posts: 8	Re: Spankeys Jetting Guide I think this need to be a sticky note. I mean how many people need help with jetting on here. I mean I have no problem with helping but you have to help yourself first. __________________________________________________ _________________________ Rahul Houston Best Florist loans with no credit check pisos vilafranca download iPhone ringtones

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