Idle

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May 24, 2007
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#1
1979 Yamaha IT400: Is bike suppose to die after a few seconds of idling? Every other bike I've had idles and stays idling with no problems. I want to be able to stop at a crossing and not have to keep the throttle turned slightly to keep the bike running. I may need to adjust the carb, 'cause as I am going down a hill or something and letting the bike slow itself down, the bike seems to lunge slightly as it decelerates. It is also hard starting after dieing from letting it idle after riding for a while. I heard it may be the main jet, but it is clean, do I need a bigger/smaller jet? How do I tell what the one is that is in there? The bike has the round-slide Mikuni Carb. Any help would be great. Thanks.
 
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May 24, 2007
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#3
It should stay idling if it is set right? What if after adjusting it, in or out, it still doesn't want to idle? The other screw, I believe the fuel one, is set to 2-1/2 turns out, if after trying to adjust the one you said, and it still doesn't idle, should I mess with that one or then what?
 
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Mar 30, 2006
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#4
Mine only idles till its fully warmed up and then it gies after a second of no throttle. 2 strokes are better off not idling, it causes plug fouling and if it idles the throttle response isnt as good.
 
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#5
In fact if set up right, A 2 stroke won't idle, quoted by a tech at Maxima oils, but it just makes it easy to idle it up a little to keep it running instead of twisting the thottle constantly.
 

fatboy570

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#6
. Id say your pilot jet is too big or the needle is set improperly. The main jet should have nothing to do with the idle circuit. You might check the float needle and seat. If this is old and worn, too much fuel can get past. Might not be a bad idea to get a new assembly. Also check the jet needle position. Usually it is in the 3rd position, which is the middle of the 5 grooves on the needle. Moving the clip up drops the needle and leans the mixture, down raises the needle and richens the mixture. Check float level, you may need a service manual to get the right level and needle postition. I have a 73 mx 250 and a 79 yz 125 and they both will idle for as long as I want, while still being able to launch off a start line. Getting a good service manual is key, I have a Clymer manual the gives all the specs I have needed so far
 
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#7
kx125412, 2 strokes can idle as long as you know how to jet the bike properly. Also, a propper jetting jop a bike should only have to use a different spark plug a year.

GoT_GreeN, you can make 2 strokes idle as long as the jetting is good.

drgriffi1, i also think it could be, pilot jet too big, sir leak, or crank seals.
 
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#8
hmm. how about the idle stop screw? This would be the one that goes into the side of the throttle valve bore, and physically stops the slide's openeing position? Sneak that in a little to leave the throttle open a hair more when the cable is released.. If you play with the air screw too much that can give you other problems.

All else failing, I would say the pilot jet could be clogged....you know, if your lugging the motor, and when letting off the throtle, it dies right away, that could be a clogged pilot jet.

By the way, I have also heard that stuff about how a 2 stroke wont idle. Every two stroke Ive ever had for the last 25 years has idled fine. And if it didnt, what the heck would you do coming down a long steep hill? Have a flame out every time and hope when you dump the clutch it will start? I mean Ive done that before by accident, but...
 
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#9
2stroke, i also belive that 2 strokes can idle great and can be lugged around in lower RPMs without fouling a plug if jetted at a 12.5:1 air to fule ratio. At this point try cleaning your airfliter, spark plug gap, correct float bowl level and no air leaks. and all of what 2stroke said.