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what could have happened?

Discussion in 'The Garage' started by a1steaksauce, Oct 20, 2019.

  1. a1steaksauce

    a1steaksauce XS400 Enthusiast

    My xs400 was running perfectly fine and then just one day it started bogging every now and then.
    I replaced the fuel filter because it was super gunked and then added clamps and it seems that the fuel isn't running quite as freely as it was before, so I am planning on just putting a straight through line and seeing if it solves the problem.

    However, now it has 2 issues. 1)once it gets hot it idles super super high (I replaced the intake manifolds about a month ago). and 2) when I'm not on the throttle it almost dies.

    An early symptom before it got this bad was that when I pulled the throttle it would bog bog bog and then sort of go. There was also a really bad fuel smell and the motorcycle sounds really different now when I start it.

    Is there anything I should check?
    I've cleaned the jets in the carb
    will check for airleaks and add a new fuel line
    replaced the spark plugs
  2. NewHavenMike

    NewHavenMike 1976 XS360C Top Contributor

    Sounds like an airleak but could be other things. Timing could be off, throttle cable could be sticking too. Could be the carbs are still dirty, they always are....

    Dont make carb adjustments when the bike is still warming up. You should ride it fairly hard for 30mins at least first.

    A decent fuel filter shouldn't impede flow enough to be a problem.

    I cant see what year your bike is so it could be the points need adjust/changed. Mechanical advance units in points bikes can freeze up, preventing smooth timing advancement and return.

    Pilots could be lean, that would cause a high idle and probably the bogging too.

    Aftermarket boots are not the best and the inner lip that the carbs lock into on the boot will tear right off pretty easily.
    buztabuzt likes this.
  3. a1steaksauce

    a1steaksauce XS400 Enthusiast

    hm ok, the bike was perfectly fine before that one day so I'm hoping that the jetting isn't the problem.
    The weather did get significantly colder (about 20 degrees) in that week so that could be affecting something?
    I'll recheck for airlocks and make sure my points are okay.
  4. tostentr

    tostentr XS400 New Member

    Hope you get it fixed soon.
  5. NewHavenMike

    NewHavenMike 1976 XS360C Top Contributor

    Btw, you should always need to use the choke lever to start the bike cold.

    I forgot to mention that the carbs probably need to be synced too.. id check this out first.

    Every time the carbs are removed this has to be verified. If the carbs arent synced, one cylinder will work harder than the other and it creates a huge imbalance.
  6. a1steaksauce

    a1steaksauce XS400 Enthusiast

    yup always used the choke to start the bike cold
    I verified the carb syncing, vacuum leaks, pilot jetting(through the fuel mixture screws on top of the manifolds), and put a direct fuel line

    the bike doesn't idle super high anymore, but I still have the weird issue of the bike idling fine and then once put into gear, it will miss a couple of strokes and the bike will not respond to throttle properly. it makes the ride jerky and it feels like it is 8-stroking if that makes any sense. it feels as though it is only getting power half of the time or something even less than that.
    What would cause this?

    one thing weird that i noticed was that at one point in my fuel mixture screw testing, i was able to run the bike with the idle screw completely down and throttle not having pressure at all.
  7. a1steaksauce

    a1steaksauce XS400 Enthusiast

    it almost feels as though the bike is stalling once i put it into gear if that gives a better visualization.

    also the day the bike really went bad, it would keep trying to die on me when i let go of the throttle. it still had the similar-to-stalling symptoms and so I just kept holding the throttle whenever i had to stop. essentially it couldn't hold an idle. i got home but i'm wondering what could have caused a symptom like that
  8. a1steaksauce

    a1steaksauce XS400 Enthusiast

    also just as extra info,
    I'm running straight pipes with pod filters (it's the way i bought it)
    with 145 mains and 45 pilot. I have the fuel mixture 3.5 turns out.
    My plugs are weird because half of it is usually blackish and sooty and the other half is a whiter tone.
  9. pcream

    pcream XS400 Enthusiast

    Half of your plug from one cylinder is one color and the other half is different? Or one plug from one cylinder looks different from the other cylinder? Got any pictures?

    If it's the former, I've not heard of that and I don't know what it could be. Draw a mark on the plug while it's screwed it so you can figure out whether the black/white is on the exhaust or intake side, maybe a valve problem?

    If it's the latter, it's probably related to the carb/sync but could potentially mean one of the cylinders is not firing, off on valve/ignition timing, or has poor compression. Do a compression test and see what the PSI is. Then add a little oil in and see if the compression improves if it's lower than spec, indicating the rings are bad.

    I would also echo other suggestions I see often here, in that you should ditch the pods and get a foam universal filter. It looks worse aesthetically, but the pods can cause inconsistent airflow that makes carb tuning difficult. I've personally had problems using pods on other bikes/carbs.
    buztabuzt likes this.
  10. Post pics. Provide other background
    Valve clearances checked? What year- does it have points to correctly time? Did you synch carbs?
    Something isn't tuned right if it ran at all with fuel/air mixture screw screwed all the way in. As mentioned, pod filters and straight pipes means more complications tuning.

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