Question on idle screw

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Jul 3, 2001
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#1
I bought my '95 300 EXC last year. It is in great shape and ran great. Still runs real good I guess except that I have no idle. I now have to have the idle screw turned all the way in. When it is cool the idle it is a little high but after the engine warms up the idle goes way down to the point where it will stall after about 15 - 30 seconds with the clutch in and no throttle. I cleaned the carb pretty well and it didn't change. Help? Thanks!
:eek:
 

fremontguy

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#2
This is a problem I can relate to. On my '95 300 I have the Idle screw turned out about 1 turn and when it's first started it will idle fast. Then it winds down just like yours, as it gets hotter. The only thing I've found to raise the idle speed is to run larger pilot jet and/or richer needle setting. For me this also increases the chances of plug fouling:silly: I am beginning to think it's not made to idle past 1 min., just a characteristic of the beast.
 

biglou

#3
Being a two-stroke newbie, I am not sure about this, but I thought I read a thread awhile back that said if you set your bike up to not idle, you would get snappier throttle response. Is there any truth to that? BTW-Mine is set up such that it will die if the throttle is not blipped continuously but I haven't adjusted the idle screw, either.
 

Shaw520

Damn Yankees
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#4
Personaly, I think running a lean pilot curcuit, (to the point where it wont idle), is not good. The engine is starving for fuel between every blip of the throttle, So,... with the throttle off, and decending long down hills, the engine relys on the pilot curcuit to keep the top end lubricated. There is no reason not to get the pilot jet crisp (right) to idle continuously with out any effect on throttle response.
 

biglou

#5
The KTM's are jetted extremely rich when stock. It's not the same as when I do 1/2 lap and it dies because I forgot to turn the petcock on, and this happens more often than I'd like to admit! There is no missing/sputtering when I just let the throttle go. It's very similar to when you hit the kill switch.

When I'm coming into a corner, or a similar situation where the motor is "freewheeling", it is still running/firing (corrrect terminology?). Doesn't the vacuum created by this continue to pull fuel into the cylinder to perpetuate this running condition? If the clutch is pulled in, THEN it will fall off and die if the throttle isn't blipped. Isn't the physical position of the slide off of it's end of travel, not the pilot jet, what dictates the idle speed? Inquiring minds want to know! :think

Any experts on the theory of operation of these circuits?
 
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#6
There sure are a lot of experts here ! That much I can see. I would be interested to here the replies you get to your question, big lou. I guess from the feedback I have gotton so far, I'm going to start with cleaning the carb very thoughly.
 
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#7
Your jetting is probably off, but on the rich side. I've had this happen on my 200 EXC, 300 EXC and GG XC250 when new with rich jetting. This is a common symptom. I'll bet your air screw has no affect either. What your doing with the idle speed screw in is lifting the slide, and forcing the needle diameter to come into play. This is the point of pilot/needle/slide cutaway overlap. There is no fine line with regard to circuit function. Post your current jetting and conditions and you'll get some answers for corrections.

Some say the Keihin carbs work best when set not to idle, and that may be true, but its a pain in woods riding, where the throttle is closed more often. The bike will stall easy when doing clutch in brake slide turns in tight trees.
 
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#8
GlennP
You hit it. That is exactly the problem I am having. I brake slide in tight woods and the bike stalls out. I will check out my settings and post them for feeback.

Thanks!
 

Jaybird

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#9
I have no problems with my Keihin 39mm and idle. When the bike is warm, I just set the air screw...usually about 1.5 turns out, then set the idle to run as low as it will go and still stay running, then give it just a lil bit more.
You need to have the bike so it will idle, no matter what type of riding you do...track or woods. Be sure you are pulling the clutch in. You may be blaming the stall on the wrong thing.
Take a quick look at that plug, it can tell you lots!