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Weird Noise When Running Bike?

Discussion in 'The Garage' started by SupsChad, Dec 19, 2021.

  1. SupsChad

    SupsChad XS400 Enthusiast

    Been troubleshooting an oil leak and finally just installed the battery again. Pulled the choke fully out as its about 30 degrees out and I don't remember the noise being there. It was idling at I think 2-3k, I don't know for sure and then at some point I heard it drop in RPM to around 1.5k without touching the choke. Thats the first time I remember hearing this noise. It sounds like a rattle more than engine knock, but I have never actually heard engine knock in person so I don't really know. I'm not saying it was not always there, just that I just now noticed it. What do you guys think this is if anything.


    P.S. After hearing this I checked to make sure each spark plug was working right, and they are. As well as I noticed while the bike was running (Before I remember hearing the sound) there was exhaust coming from the front of the bike near the clutch cover I think (Circular cover on left side of the bike). I did see that the left exhaust had a leak near the connection of the pipe and the muffler so maybe the smoke is traveling to the front. Or it could just be residue burning off when I over sprayed with penetrating oil, I dunno.
  2. Buddha

    Buddha XS400 Addict Top Contributor

    "Been troubleshooting an oil leak and finally just installed the battery again."
    Thats vague information, did you have anything apart on the engine to fix the oil leak?

    Listened to the video and the 'rattle' sounds like it's in sync with engine rpm.

    Did you pull the plugs to see if there is any damage to the electrode or the porcelain?

    There may be a chance your engine ingested something and it's rattling around in the combustion chamber, hope I'm wrong.
  3. SupsChad

    SupsChad XS400 Enthusiast

    The oil leak was from the push rod, I'm pretty sure that's the name of it but its the rod the clutch lever is connected to. All I did was remove the side cover that's over the front sprocket. And then I sprayed some engine degreeser on a rag and cleaned up the inside a bit. And yes I went back out there because a buddy of mine asked if its in sync with the rpm and it is. It sort of sounds like its coming from the top end of the motor but I cant tell as sound can be deceiving sometimes. My friend thought it could be the piston connection rod has to much slack and is is "bouncing up and down" on the crank. I think I wont know until I take the engine out and look inside. And I dont beleive its the piston hitting the top because from what I seen that has a lower thud to it. As for the plugs, ya I pulled them. The outer white ceramic had no damage and the tips looked fine. They did have some carbon buildup on them but they weren't running lean and it had spark on both plugs.
  4. xschris

    xschris XS400 Guru Top Contributor

    Sounds like your valves out of adjustment. There's a lot of threads on this in the forum as people sometimes don't set them correctly. What weight oil is in it? Running a lighter than the stock 20-w50 can cause extra noise. Always sync the carbs with the engine warm and the rpm's at 1200. No more no less.
    Last edited: Dec 21, 2021
    JPaganel likes this.
  5. Buddha

    Buddha XS400 Addict Top Contributor

    That's good, debris inside the combustion chamber would raise havoc on the plugs, so I would say there's nothing wrong inside the cylinders.
  6. SupsChad

    SupsChad XS400 Enthusiast

    Sorry just now seeing this. I dont know what oil was in the bike. I hadent rode it or really run the bike since I bought it. I just knew that it was not low on oil. But I can see when I take the head off if the valves are in spec

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