bike running rich

[Coop]

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.

[Chokey]

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.

[kawi250]

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

[riffraff]

I would think that if it were jetted correctly that only the idle screw would be needed to get it to idle

[evo550]

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.

[TotalNZ]

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.

[ford832]

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?

[evo550]

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?

[ford832]

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.

[kawi250]

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?

[ford832]

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

[kawi250]

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 !

[riffraff]

What kind of carb do you have?

[G-MONEY]

I guess that should have been the first question we asked what kind of carb do you have?

[ford832]

As long as it's a modern day machine it's fairly irrelevant as the same principles and procedures apply.