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RD 125 DX '81 - won't idle


Mastiff
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Well, it will idle for a little while, but then it just dies. And that will happen if I let it slow down too much without engaging the clutch and rev it a bit. Where should I start to look for this problem? The bike should be in good shape, it has been checked out in a Yamaha garage before I got it. Do I need to do a carb job on this thing, or can it be something easier?

It happens on both warm and cold enine, and it will run for maybe 10 seconds on idle before it slowly starts dying. It really doesn't remind me of anything I have had before on my 350's. But I'm still thinking carbs or something else in the fuel system, not electrical. Any objections?

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Yes it is. Thanks! By balancing I hope you mean using the "eye" on the barrel (I would guess there is one, like I have on my RD's) to see that a certain level of throttle moves the pistons to the same point? I really didn't think it could be the idle screws because it idles for some seconds before it starts to die, and I assumed that tightening the screws would only make it idle far to high. But maybe not? Worth a shot at least.

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Yes it is. Thanks! By balancing I hope you mean using the "eye" on the barrel (I would guess there is one, like I have on my RD's) to see that a certain level of throttle moves the pistons to the same point? I really didn't think it could be the idle screws because it idles for some seconds before it starts to die, and I assumed that tightening the screws would only make it idle far to high. But maybe not? Worth a shot at least.

I dont think there is a window on those carbs you have to do it by feel,

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If it is the same as on my old 1980 RD200DX I had which I think it is you should find a window on the outside of each carb . What you do is open the throttle fully and look in the window and adjust the cable using the adjuster on the carb top until you see the line of the slide in the centre of the each window doing this before you set the throttle stop screws.If you strip the carbs to make sure the jets are clear "especially the pilot jets" make sure you connect the pipe between the carbs that joins the choke system and you reconnect the oil pump feed pipes on the carbs and you get the throttle slides in the right carbs with the cutaway on the slide facing back towards the airbox.

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If it is the same as on my old 1980 RD200DX I had which I think it is you should find a window on the outside of each carb . What you do is open the throttle fully and look in the window and adjust the cable using the adjuster on the carb top until you see the line of the slide in the centre of the each window doing this before you set the throttle stop screws.If you strip the carbs to make sure the jets are clear "especially the pilot jets" make sure you connect the pipe between the carbs that joins the choke system and you reconnect the oil pump feed pipes on the carbs and you get the throttle slides in the right carbs with the cutaway on the slide facing back towards the airbox.

OK if theres a window thats good, I was going of my earlier RD that didnt have one.

You have to open the throttle to do the window alignment dont you? so idle can be done first or last it doesnt matter on that type. However with a carb without windows it must be done first.

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