Two Stroke Motocross
Two Stroke Motocross Forum => Technical => Topic started by: kawi250 on May 06, 2010, 04:05:48 PM
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OK so here's another question for those brave enough to attempt to answer. My bike was idleing to low and would die in about a minute but rides fine and if you give it gas while idleing it wont die. I switched the plug today and it idles a lot better and sounds better too. The old plug was black and even had some almost liquid exhaust on it, to lean the Carb would I just back the air screw out? Going slowly and checking how it runs? Or should I keep it a little rich and just change the plug more? Thanks for the help
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Take it for a ride to warm it up then set your idle to about 1200 rpm with the idle screw then adjust your air screw in and out until you get the highest rpm.Once there,ck your setting.If you're under a 1/2 turn out,you need to go up on your pilot(richer).If you're over 1 1/2 turns out,you need to go down on your pilot(leaner).Once done,set your idle back down.If you can idle for a minute you have your idle turned too high.Properly set,and for best response,a 2t mx should idle for 5-6 seconds before it quits.If you let it idle for a minute,even if it's lean,the plug will be black.
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Sounds like your air filter maybe dirty or resticted in some fashion.When the engine can't get enough air the vacuum or negative pressure is increased which draws more fuel through the main jet.hence the rich running.Give it a good cleaning and let us know what you get.
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Most bikes don't idle on the main ;)
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Most bikes get richer when the weather gets hotter..........just sayin :-X
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How old is your bike? Might be time for a new float needle and seat assy..
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Alright I actually didn't know that a 2t idleing correctly only idled for 5 to 6 seconds before dying, and the point about not idling in the main goes along with that. I changed the plug and it ran and sounded a lot better. As for the air filter it was cleaned maybe 3 hours ago and still looks fine. I think I was being paranoid about it running rich. It idles for a short period of time without dying and no gas but sounds good with the new plug I think I was just being over concerned
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Alright I actually didn't know that a 2t idleing correctly only idled for 5 to 6 seconds before dying,
That's nothing more than a myth perpetuated on sites such as this by people that are too lazy or incapable of jetting their bikes correctly. A properly jetted two-stroke will idle indefinitely with no loading up or plug fouling.
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it does last for much longer now that i have changed the plug and i will check to see if it continues to run good or becomes like it was before. if it does i'll just try the air and fuel screws
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Alright I actually didn't know that a 2t idleing correctly only idled for 5 to 6 seconds before dying,
That's nothing more than a myth perpetuated on sites such as this by people that are too lazy or incapable of jetting their bikes correctly. A properly jetted two-stroke will idle indefinitely with no loading up or plug fouling.
Imagine my surprise to find I'm too incapable and lazy to jet my own bike.As always,however,I'm willing to learn.My record isn't the best,my last 4 2t bikes having fouled exactly 2 plugs altogether.One was a dud(lasted 30 sec)and the other was from following a friends young fella on his 50 through the woods on a stinking hot day(no,I wasn't jetted for that)
Interestingly enough,my 2t lawn boy mower will happily idle all day long while I,not so happily,push it around.I always thought it magic somehow.
It has also never really occurred to me that the yz and lawn boy have the same engine design and were designed to operate within the exact same parameters.I guess a 2t is a 2t regardless of anything else.
Oh well,that's just more work for me I guess.Time to go rip the carb off and change to a leaner pilot and higher idle setting.I know I'll lose some response but it will be worth it to have my improperly set up bike idle all day long-as it no doubt should-because that's what the engineers designed it for.Many thanks.
Before I do though,I must go hit some other sites to see what mechanical bits of info I can find.It will likely serve me well at work tomorrow.Thanks again.
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You can be as sarcastic as you want. That doesn't change the fact that there is absolutely no reason why a two-stroke should not be able to sustain an idle.
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You can be as sarcastic as you want. That doesn't change the fact that there is absolutely no reason why a two-stroke should not be able to sustain an idle.
Thanks,I believe I will be :D
What I initially said was..... "Properly set,and for best response,"A 2T MX SHOULD IDLE FOR 5-6 SECONDS BEFORE IT QUITS"
What this means then,is that,when properly set,s 2t mx should idle for 5-6 seconds before it quits.
Nowhere did I say a 2t cannot be made to idle.If,for some reason,you need yours to do so,by all means-do it-it's easy enough.But,well,see above.
My original read on Kawi250's original post was that there is likely nothing wrong with his bike at all-other than perhaps a slightly high idle-or a minor air screw adjustment.I tried to convey the proper way,as best I know,how to properly set it.And no,I don't go jerking around on message boards trying to find mechanical drivel.Rightly or wrongly,this is what I do from my experience-it works for me,and likely will for him.
I am however,somewhat surprised that you call me lazy and incapable and then expect some sort of "touchy-feely" response.
I've always been more than willing to be proven wrong as it's the best way to learn anything in detail.If you feel so inclined,without dredging up internet crap like "this guy says this or that guy says that"by all means,go ahead.I'm listening.
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I always set my bike up so they don't idle. Nothing worse then crashing your brains out and having your bike idling merrily away in a mudhole somewhere.
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Why would you want to idle your bike for a minute anyway?
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You can be as sarcastic as you want. That doesn't change the fact that there is absolutely no reason why a two-stroke should not be able to sustain an idle.
Thanks,I believe I will be :D
What I initially said was..... "Properly set,and for best response,"A 2T MX SHOULD IDLE FOR 5-6 SECONDS BEFORE IT QUITS"
What this means then,is that,when properly set,s 2t mx should idle for 5-6 seconds before it quits.
Nowhere did I say a 2t cannot be made to idle.If,for some reason,you need yours to do so,by all means-do it-it's easy enough.But,well,see above.
My original read on Kawi250's original post was that there is likely nothing wrong with his bike at all-other than perhaps a slightly high idle-or a minor air screw adjustment.I tried to convey the proper way,as best I know,how to properly set it.And no,I don't go jerking around on message boards trying to find mechanical drivel.Rightly or wrongly,this is what I do from my experience-it works for me,and likely will for him.
I am however,somewhat surprised that you call me lazy and incapable and then expect some sort of "touchy-feely" response.
I've always been more than willing to be proven wrong as it's the best way to learn anything in detail.If you feel so inclined,without dredging up internet crap like "this guy says this or that guy says that"by all means,go ahead.I'm listening.
I hate to break the news to you, but not everything is directed at you personally. Nowhere in my posts did I directly implicate you, it was stated in the most general of terms. If you choose to not have your bike idle that is your perogative, and you aren't alone. But don't tell people that a two-stroke shouldn't or can't sustain an idle as if it were the gospel, because it just ain't so. That's no different than telling people that plug fouling is caused by too much oil in the mix, or calling Wiseco's "Seizcos". Misinformation such as that perpetuates myths and stereotypes that have no merits or basis in facts.
I am sorry if you took personal offense at my post, it was not intended as such, nor was it targeted directly at you personally. But I stand by what I said. There is absolutely no reason why a two-stroke can not or should not be able to sustain an idle. The idea that a two-stroke "is not supposed to idle" (why in the world do they have an idle circuit then?) is nothing more than misinformation that I see repeated time and time again on discussion boards, and I try to correct it when I can. After all, isn't giving out factually correct information supposed to be the point of this board?
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The idea that a two-stroke "is not supposed to idle" (why in the world do they have an idle circuit then?) is nothing more than misinformation that I see repeated time and time again on discussion boards, and I try to correct it when I can. After all, isn't giving out factually correct information supposed to be the point of this board?
Honestly Chokey, Eric Gorr said in his first book (maybe others, I was only ever given the first one) that a two stroke MX bike should not idle when set up properly. So I wouldn't consider that misinformation, just difference of opinion.
Since I trail ride with my nephew a lot (stop often to wait) I like my bikes to idle, so I jet them accordingly. I ride a KX125 in the woods and have yet to foul a plug.
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The idea that a two-stroke "is not supposed to idle" (why in the world do they have an idle circuit then?) is nothing more than misinformation that I see repeated time and time again on discussion boards, and I try to correct it when I can. After all, isn't giving out factually correct information supposed to be the point of this board?
Honestly Chokey, Eric Gorr said in his first book (maybe others, I was only ever given the first one) that a two stroke MX bike should not idle when set up properly. So I wouldn't consider that misinformation, just difference of opinion.
Since I trail ride with my nephew a lot (stop often to wait) I like my bikes to idle, so I jet them accordingly. I ride a KX125 in the woods and have yet to foul a plug.
OK, I'll accept the "difference of opinion" for this idea. And I do admit that there is a small advantage in throttle response with certain carbs (primarily Mikunis that don't use a seperate pilot circuit) when they are set to not idle. But by far the most common modern two-stroke carb is the Keihin PWK. The PWK is an excellent carb with a very well designed pilot circuit, and you would be hard pressed to tell any difference whatsoever in throttle reponse with it set to not idle.
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so then if i am to get the bike idling correctly and the changing of the plugs helped it idle much better i can assume its running a little to rich correct? then i would start at the air screw? and back it out to lean the mixture? in case you can't tell i dont know much about this process this is my second dirt bike and my first was a four stroke that never need much adjustment so i dont have experience. any advice is greatly appreciated
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I would think that if it were jetted correctly that only the idle screw would be needed to get it to idle
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I set mine to idle, nothing worse than sitting on the line, trying to fit your goggles and keep your bike running at the same time. Not sure why it would be a problem, did Eric Gorr say why?
Back when 500 2 t's rules the roost some riders prefered them not to idle too prevent them overshooting a berm or corner.
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All my bikes are jetted pretty well and they all will also idle indefinately, i'm open to learning new things though so could someone please explain why a 2t MX bike shouldn't idle.
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It's certainly not that it won't work that way,in the same way that a bike jetted slightly rich will work just fine.The key is "for best response"Granted,it's not a huge difference,but little differences add up to bigger ones.It all depends what you're after-as good as it can be or close enough.
Chokey-I've never claimed that oil causes plug fouling and for the record,I like wiseco.I appreciate your mission to educate the great unwashed masses but the fact that it's your opinion doesn't make it "factually correct"any more than mine does.BTW,a PWK is my favorite carb,and most of my 2t's have run them.
Sachs brings up a good point as well.Mine dies pretty much as soon as it hits the ground,the berg would run forever until I put on a tether,to avoid chewing up bits of myself.
Kawi 250,you're right,backing it out will lean it out as it's an air screw.On 4t,backing it out richens it up as it's a fuel screw.Not to be confused with a small gas 2t which has an airscrew(so called)as well but generally backing it out richens it up.-Clear as mud eh? ;D
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I'm still confused...Idle isn't set by jetting (unless it's drastically lean).
Idle is determined by the position of the slide, which is set by the idle screw, so wouldn't a perfectly jetted 2 stroke not idle because the slide is fully closed, not because it's perfectly jetted?
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You're right but you need to remember that even when the slide is fully closed,it's not as air will still pass by.
If you look at the back of your slide you will see a cutaway.This affects the jetting off the bottom due to the change in air velocity that various cutaways produce.The less cutaway you have,the richer you are off the bottom.Turning the idle screw in partially raises the slide in the exact same way that twisting the throttle slightly does.The problem is,by doing this,you are partially negating the desired effect of the slide cutaway (especially if you turn it too far)and its inherent effect on the pilot circuit at low rpm.This also affects the starting which can lead a person to change their pilot based on how it starts when in fact the setting may be fine,but masked by the idle setting.Once the pilot is changed incorrectly to compensate,performance will suffer.It's not a big deal but it makes a difference just the same.If it were me,I'd set it up as per my first post then if you want it to idle,crank the screw in a bit.Honestly,it's just not that big of deal(provided you're jetted correctly before you turn the idle up) but it's the proper procedure just the same-especially if you're somewhat of a nitpicker about your bike-like me. ::)
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haha clear as mud is the best way to put it. So i'll just start adjusting it slowly and checking how the bike runs with each adjustment correct? by adjusting the idle screw i cannot make the engine run way too lean and blow something up, that would be if i adjusted the jetting in the carb right?
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One thing that I forgot to mention that I likely should have-don't think the pilot circuit only affects the bottom end.There is a fair bit of crossover as you increase the rpm's and head toward the mid.For instance,as you start accelerating from idle toward the mid,your pilot still has an effect but it lessens as rpms increase and you start coming into the mid.A pilot circuit that is misjetted therefore,has a fair effect on your low to mid transition-hence the response issue.
Now then,Kawi 250,the initial post is the best way to be precise but if you want to play around a little and get a feel for it,that's not a bad idea either.
With the bike shut off,put a little paint or marker mark on one end of the slot in the airscrew then a corresponding one on the carb body.After that,turn the screw to the right(clockwise)counting turns as you go(ie 1/4,1/2,/3/4,1,11/4 and so on) until it LIGHTLY stops-don't force it.From there return to your original position.Ideally you should be in the 1 to 2 turns out range(if not,don't worry about it).Start the bike then warm it up fully.Once you've done that,turn your idle down so it's just idling if you were higher than that.
From here you can play around with the airscrew all you want as you won't hurt anything.
Once you change the airscrew setting,it will take a few seconds for this to become noticeable so rev it up a couple times and then let it settle down for a few seconds.
To get a feel for a rich setting,turn your screw about a 1/2 turn out from seated,start the bike and try it.It has sort of a "heavy" sound and feel.Ride it a bit this way starting from a stop and slowly accelerating,then try it accelerating normally.Once you get a feel for that,turn the airscrew about 2 1/2 turns out(leaner) and try it again.
This will give you a feel for both extremes.
From there,adjust it 1/4 turn at a time or so between these settings,ride it from stopped while mildly accelerating,then quickly accelerating and keep repeating until you get to the best setting for power and response.
Once you do,shut the bike off and count the turns again as you turn the screw in clockwise.Once you have a number,return it back to that setting and let us know what your number is and we'll tell you where to go from there.If your best results are farther out than 2 1/2 or farther in than one you have a little jetting to do.Fun,fun and there's power to be had,and you can tune it yourself.Who could ask for any more than that 8)
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I'll try to get around to it tomorrow and let you know how it turns out. Thanks a bunch for the detailed help it is much appreciated !
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What kind of carb do you have?
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I guess that should have been the first question we asked what kind of carb do you have?
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As long as it's a modern day machine it's fairly irrelevant as the same principles and procedures apply.
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Well if it's a Mikuni I know the have a great manual available that explains everything with step by step procedures, I've got it saved on my computer along with the 2 stroke tuners handbook.
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it is a 05 kx250, the carb is a keihin pwk38s
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Report? :)
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Ok I just finished initially the screw was like two and a half turns out. I just bought it and the guy said he kept it rich to be safe so I unscrewed it two full turns out and it ripped I swear I had better throttle response and harder power bans. I was worried it sounded like it was idleig too high though so I turned it to the right two quarter turns or a half and it sounds as I think it should and idles all day long. So now I am roughly one and a half turns out and I think I'm good to go! Was I right in richening it since I thought it was idleing to high?
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My last post was a little rushed and im still confused at how the air screw was so far out to begin with? turning it to the right richened it and i started by turning it all the way to the right. then backed it out 2 turns which is when i noticed a power difference(or think i did anyways) the bike was ideling better but after i got back and listened to it idle without a helmet on i was concerned it was ideling to high, which is when i richened it or turned the screw to the right a half turn. now it seems to be idleing as it should and isn't dying like it was before. My question is should i go by sound? or performance? i have yet to ride it after the half turn in since i had something to do but plan on test riding the new position tomorrow but thought it was safe to assume that since the bike is idleing good it should ride good as well
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Firstly,the last guy had it leaned out if he was 2 1/2 turns out.By turning it 2 out you richened it a bit.If your idle dropped when you turned it in to 1 1/2 you've gone too far.For your airscrew setting,you want the highest idle-2 turns by the sound of it.Once there,turn your "idle screw"(above the Keihin marking-likely black plastic head with a spring behind it directly to the rear of the bike from your choke knob)to the left(counterclockwise) until the idle drops to where you want it.The airscrew shouldn't be used to set your idle as this gives you the wrong setting.
If two turns out turns out to be your best setting you're in range but almost at the lean extent.If the temperature where you ride goes up much more in the summer you can go out to about 2 1/2 then but after that you will need to switch to one size smaller(leaner)pilot jet.
As for sound/feel/performance setting,I set it first by rpm/sound then ride it.After that,try turning it in 1/8 turn or so to see if it's a bit better-if not,go out the same and try it again.If both are worse,return to your original setting.Sometimes the best performance will be slightly to one side or the other of the max rpm setting.Of course,once the temp changes you'll have to readjust to maintain it.Colder temps-richer/hotter temps-leaner.
That's why it's good to have the bike jetted for your usual riding temps.That way,slight temp changes can be taken care of quickly with just an airscrew adjustment.Eg.,if say your usual riding temp is 70'F and you have a pilot jet in it that allows you have your screw at 1 1/2 turns out you can typically go about 1 turn out for 60' or 2 turns out for 80'.More or less anyway.
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haha ok this is going to show how new to this i am. the only screw i adjusted was the screw with the black plastic head and that was the screw that 2 and a half turns out. i did the steps i listed before to the idle screw (with the black plastic head) and now that screw is set at just about 1 and a half turns out. I guess i was not specific enough in my original post. the bike was never bogging just idling to low, and the plugs were getting really black and almost had liquid exhaust on them. so maybe my problem was just the idle screw? i hope this helps better clarify what i adjusted
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and for future reference can you give me any helpful hints to identify my air screw? please excuse the fact that i am such a noob haha
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The idle mixture screw is below the "N" in Keihin.
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What tmkiwi said.It's a little brass screw that sits flush with the carb.Try it agian with that one. :)
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Ok I'll give that a shot. And I shouldn't be worried about the idle screw I adjusted last time right? Since I Haha it idleing where I want it I can re adjust it after I lean the bike out.
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Turn the idle down as low as you can,then set your airscrew.Once done,put your idle where you want it.
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Ok two last questions before I go try it. If the bike was running good and just idling rich and low isn't it a possibility that only the idle screw needed to be adjusted? And second turning the idle low is richening the idle and turning that screw to the right correct?
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Hey kawi250 just try this,warm the bike up hold the throttle to a fast idle 1000 r.p.ms then adjust the brass screw in and out till it sounds the best to you then set the plastic one to your likeing. You can do this as much as you want.From cool morning rides to hot afternoon rides to dial in your bike. If you have burbbling (rich) or surging (lean) in your throttle range let us know let us know then we can zero in on pilot jets,mains or needles.
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when setting the idle how will I know what's low or high? do i turn it down meaning really rich and high meaning really lean and tell by sound? im gonna give it a go tomorrow to get ready for southwick this sunday!
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Turning your black plastic idle screw has no bearing on rich or lean-it simply raises the slide a little-exactly the same as when you twist the throttle a little bit.Once warmed up,turn your idle screw to the left until the bike quits,then turn it to the right a bit,start it up and set the airscrew.Once done,set the idle where you like-I like mine to stall after a few seconds but some like them to idle.Regardless,keep the lowest idle setting you can.
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OK so this time I checked the position of the air screw and it was one turn out. So I turned it to the left a quarter turn and rode it from there it seemed a little better but rode pretty much the same. It isn't bogging or anything and it seemed to have good bottom end power. I then readjusted my idle to a lower idle because the last time I set it high I felt it made the bike bog if it sat too long. Before I ride next should I put a new plug in and check it at the end of the day to track my progress? And thanks again for all the help now I can get my bike running correctly any time I want haha
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Your air screw should be about 1-1/2 turns out; anything less than 1-1/2 or more than 2 and I always re-jet.
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Print this out and study it. It will help you to understand jetting.
I highlighted the section that deals with the pilot circuit for you.
Spanky's Jetting 101:
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. Hard starting when hot or cold, poor response when opening the throttle, reluctance to idle, all of these are symptoms of an improperly sized pilot jet or incorrectly adjusted air screw.
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. An engine that is jetted too rich will have combustion temperatures that are too low to burn the fuel and oil effectively, leading to deposits and wet fouling of the plugs.
Do you have spooge? There are the rare instances where a mechanical issue, such as a leaking wet-side crank seal, can cause spooge. But, by and large, this isnâ??t the case. In most instances, spooge is caused by rich jetting. It has nothing to do with how much oil you mix in the gas, or how hard you ride. An engine that is jetted too rich will have combustion temperatures that are too low to burn the fuel and oil effectively, resulting in deposits, plug fouling, and spooge. Spooge is nothing more than unburned fuel and oil entering the exhaust.
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. Someone with a good understanding of jetting can get you in the ball park, but you need to do the testing to determine the correct jetting yourself if you want it right.
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, because 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 re-jet 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.
All jet testing must be done with the engine at full operating temperature.
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 idling. Turn the air screw 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. If your engine doesnâ??t respond to air screw changes, then you either have a dirty carb, or the pilot jet is way too rich. When the pilot jet is way too rich, you are forced to use the idle screw to open the slide so far in order to keep the engine running that the pilot circuit is partially bypassed, and the engine is actually starting to draw fuel through the needle jet.
Once you have determined (and installed it if it's necessary 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. A too-rich needle can often be felt simply when revving the bike on the stand. The bike will sound rough and raspy when blipping the throttle on the stand. A correctly jetted bike should rev cleanly and crisply.
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.
Please note that, when reading plugs, the tip of the insulator, threads, etc. are meaningless for jetting purposes. They can tell you a lot of things, but jetting isnâ??t one of them. Only the mixture ring at the very base of the insulator, inside the threads, can tell you anything about the jetting.
These links should help you to understand reading plugs:
(http://cdn.thumpertalk.com/3/35/35507100_sparkplug.gif)
(http://cdn.thumpertalk.com/d/db/db7f02ab_sparkplug%20b-w%20.gif)
The slide is also a tuning variable for jetting, affecting the throttle range from 1/8 throttle to approximately 1/3 throttle. If you canâ??t clean up the small-throttle jetting on your bike no matter how lean you go with the pilot or the needle, the slide is the next step. But few bikes need leaner slides.
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, and 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. Their purpose is the same, they just do it in different ways.
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OK so this time I checked the position of the air screw and it was one turn out. So I turned it to the left a quarter turn and rode it from there it seemed a little better but rode pretty much the same. It isn't bogging or anything and it seemed to have good bottom end power. I then readjusted my idle to a lower idle because the last time I set it high I felt it made the bike bog if it sat too long. Before I ride next should I put a new plug in and check it at the end of the day to track my progress? And thanks again for all the help now I can get my bike running correctly any time I want haha
Try turning it 1 1/2 out to see what you get,then try at 2(I like to go in 1/2 turn increments then fine tune from there).Ideally,go back to the first post and do it that way but if not,try it at various settings. 1/4 turn different than what you had won't usually make a huge noticeable difference in a "seat of the pants sort of way"
As for your plug,I'd leave the same one in.Plug chops are great but checking it after a ride won't won't tell you that much unless you're super rich or super lean everywhere.
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All my bikes are jetted pretty well and they all will also idle indefinately, i'm open to learning new things though so could someone please explain why a 2t MX bike shouldn't idle.
I know the factory Yamaha's were set not to idle; I would guess most of the factory and top pro ones did not.
Is was done for a couple reasons, to help off idle throttle response and help with jetting. My '06 YZ250 will idle for about 15 seconds (I am not in serach of that last bit of response as I can't tell the difference ;D ) This wasn't done by leaning it to where it wouldn't idle, the pilot was set correctly but my understanding was the throttle stop screw was set for no idle.
I used to have a good article by Dick Lechien (Ron Lechien's father) on setting up the idle, I'll se if I can find it or a link to it).
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What I like to see for a main jet chop. Nice ring with just a hint of color on the tip.
(http://img.photobucket.com/albums/v606/TRexRacing/plug1.jpg)
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Howdy, fellows! I looked through the article and the main question worrying me is:
DOES the air screw really affect mid and top-end throttle response??? I've got Keihin and they say the air screw can only affect from zero-opening to 1\8 opened throttle. What do you think?
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All circuits are active at WFO. The lower circuits are contributing but at a small level. The influence is small enough that unless a problem occurs at WFO after changing the pilot or needle it can be ignored. The only time I've seen it cause problems is on highly tuned big engines. The chart you see about a circuit's effectiveness is about it's usable influence. Generally if you are happy with the way it runs you're probably OK.
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Well Kawi250,what was your final result? :)
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To be honest I am still trying out new settings and the weather has changed and become hotter and more humid so I'm still trying to catch up with it. I did ride southwick last Sunday though and the bike was running awesome tons of power even in the lower rpms. It also got right up to the top of every gear with the slightest crack of the throttle. I still plan on adjusting it again in the near future but at least now I know how to correctly do that haha. Thanks to all for the help
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Good stuff.You always have to adjust when your temp/pressure/elevation changes but you're certainly ahead of most 8).A guy I used to ride with always raved about how good his KX ran spring/fall as compared to the summer though he didn't know why.You couldn't convince him to tune it though.When he sold the bike,his carb/suspension had the exact settings as when it rolled off the showroom floor.You'd be surprised how common this is.
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I understand that fella!!! Nothing can be worse than unmounting the carb with bare hands at minus 20 C... All pipes, hoses, intake behave like concrete. Yak. Hate that.
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Its worth while to understand especially when its really fairly simple to do when before I thought it was a complicated and hassle to dial in
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That IS comlplicated, i mean, not unmounting the carb but installing it BACK. :( The rubber hoses are very stiff.
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how many hoses do you have? should only be the 1 big one coming from the tank and a few little vent hoses.
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I'm sorry? I have two hoses at each side of the carb, one in the bottom - and they all are against overfilling.
I didn't mean hoses actually. I meant that large rubber pipe going from intake to carb and tghe smaller one from carb to the cylinder.
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YEAH, BABY!!!! I GOT MY BIKE JETTED TODAY!!!! NOW I WON'T TOUCH THE ENGINE TILL WINTER!!!!
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So for an even more updated post I just checked the plug since adjusting the air screw and its a ton better! I can even still see some of the white in the inside of the plug and really think I can feel the difference I've been ripping around in second and third and its been hauling ass thanks again guys!
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Special thanks to ford832 I basically used your instructions with a little of other people's but yours helped quite a bit
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Glad to help.Kudos to you for putting out the time/effort/interest to get it right. :)
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Thank you very much.