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Trouble with XS400 idle now.


johnsnownw
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Okay,

So, now that I got a new battery she will start up just fine. The suggestion was made that I should seat my mixture screws and turn back 3.5 times. Well, I've done that and can get the bike to idle in neutral around 1200 rpm, but only when I tightened the idle screw quite a bit more than it had been before. Now the bike seems to be popping quite a bit, and idle rough. It also seems to knock quite a bit, when I don't think it did before this. It should be noted that I filled the tank with 92 octane fuel.

Any suggestions?

Aaron

UPDATE: So, the knocking seems to be coming from the gas tank, in fact, if I move the petcock lever to RES, the knocking is louder than when on "ON". The knocking speeds up when the throttle is pulled.

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is your tank alittle loose and vibrating with the rough idle? I don't see how the petcok being on RES would effect it other then the slightest in wieght transfer, you may also want to pull the tank off and check the rubber/foam under it, not sure what they used on this bike if anything at all, if they did it could have degraded over time if not then it's a good idea to add some so the tank and frame don't bump and rub, I had an issue on my YZ80 as a kid cause the clutch cable also ran between the tank and frame and would rub.

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Sounds like a vacuum leak at the petcock....another reason I got ride of the vacuum operated petcock. Spray some WD04- around the back side of the petcock when it is running and see if the sound changes.

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Sounds like a vacuum leak at the petcock....another reason I got ride of the vacuum operated petcock. Spray some WD04- around the back side of the petcock when it is running and see if the sound changes.

Well, I ended up just ordering a rebuild kit for it. The o-ring for the lever was broken, but the diaphragm looked okay, but it's getting replaced anyway.

Also decided to tear down the carbs and clean them, since I'm unsure of when the last cleaning was done. Not to mention that when I unscrewed the float bowl plug the gas had a rusty color to it.

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Well, I may have figured out why the bike wasn't idling correctly. Both mixture screws were missing their O-rings. They should really list those parts in the Haynes manual, I only found out while perusing MikesXS.

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