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Novice here. Need diagnosis.

Discussion in 'The Garage' started by Rocktech, Nov 10, 2020.

  1. Rocktech

    Rocktech XS400 Member

    Hi all, I just bought a a 1980 xs400 special. I love everything about it. Except for the fact that it died the day after I drove it home. It kept acting like it had run out of fuel. (Yes there was fuel in it and yes I switched it to res.)

    All that to say, I’m pretty handy, though this is my first bike. So after research and not being able to contact any bike mechanic nearby. I started with what I knew, an oil change. Then I ventured into cleaning the air filter and then the carbs. Cleaned the carbs, and replaced the boots and vacuum hose to the petcock. Here is what I have noticed. Maybe they are separate and maybe not:
    1. It idled fine for a few min off choke, I was letting it warm up and then out of nowhere it rev’ed itself up to around 5k rpm and got stuck there. After I shut it off, I started again, idled fine. But whenever I blip the throttle it revs up again and sticks around 5k. Throttle cable is not getting stuck, it is snapping back. What causes this?

    2. After startup, I noticed cold clean oil dripping from under the gear box.where the the wires come down to the back left of the oil screen.

    3. I noticed really mucky oil and burning oil smell coming out of the (if you are sitting on the motorcycle) left header. Where it connects to the exhaust. And there is mucky all around where the spark plug goes in on that left side.

    any next steps in any of that would be helpful as I want to learn to work on this motorcycle myself. And the only mechanic that finally replied is booked till January. The goal is just to get the bike running reliably to get to work and back before adding mods.
    Thank you,
  2. Spitfire_X24

    Spitfire_X24 XS400 Enthusiast

    When you say you cleaned the carbs, were they removed and completely disassembled? The 5K idle sticking issue with no throttle cable sticking seems like an internal carb issue.
    That’s a safety issue and I do not recommend riding until this is sorted out.
    The fuel by the spark plug, what does the spark plug look like and is it torqued properly?
    The other burning smell, by the header, if there are things leaking and your plugs aren’t torqued, or you have a bad head gasket and your header gasket isn’t sealed properly...could be a number of issues there.
    Good luck sir.
  3. amc49

    amc49 XS400 Addict

    Run a compression test as so many of you do this.........buy a bike with no provenance and a worn out engine. all effort expended is then wasted.

    The throttle hang is from idle opening butterfly too much to activate the slide, often done when engine is dead wore out. Oil in the exhaust stream is more evidence of same thing.
  4. Rocktech

    Rocktech XS400 Member

    Heard, Thank you.
    I am a novice but I am not afraid of the work that a rebuild will take, if that will help. I just ask for guidence and i will keep posting updates. So thank you for that. So far compression test is top of my list. Ill do that after the rain lets up and get back to you!
  5. Rocktech

    Rocktech XS400 Member

    Oh, sorry I forgot to mention that. Yes, I am not riding it right now. but of corse i would like to as soon as I can :)
    I did take them all apart, after the engine rev problem and it is still an issue after words. My next thought as far as carbs go is to get these from mikes. https://www.mikesxs.net/yamaha-xs65..._WVSGTIfejbq23PjM8-R50tn_mDQVpOBoCWBcQAvD_BwE 1. i know they will work. and 2. I eventually wanted to put pods on anyway. What are your thoughts?
  6. amc49

    amc49 XS400 Addict

    Deeper into the hole we go...................with that link now suspecting you are a spammer. You absolutely don't know if they will work, if you did the other ones would be working.

    Until you prove out the compression you risk a $400 more expensive dead engine. New carbs will not fix a dead engine yet so many think they do.

    Hey, yours and do with it as you will. I see it all day long. 'It must be the carbs that are the problem', the premiere male testosterone issue of our age. How I got motorcycle after motorcycle given to me for free.

    What happened to this?.............

    'The goal is just to get the bike running reliably to get to work and back before adding mods.'
  7. Rocktech

    Rocktech XS400 Member

    Woah, brother. I don’t understand what I did to deserve such attitude. I’m sorry if I offended you in some way.

    I am simply a novice learning all I can, and willing to put in the work and time it takes to get her up and running.

    Thank you for your advice, I will definitely do a compression test before moving forward. Feel free not to comment on this post again.
  8. amc49

    amc49 XS400 Addict

    I won't if you don't value it. That was just me being me. Most do not want to be around if I really get mad, which I am nowhere near here. The spammer comment was simply because a hill of it showing up lately and the post could have been that. My bad.

    Feel free to ignore me possibly saving you $400 there, I know it's burning holes in your pocket. If your engine is off then it could be the worst thing you could do, high perf parts never fix basic problems and often make them worse. Take it from somebody who has built countless engines and many non-stock from the word go. You have what easily could be carb issues and wanting to complicate them worse with new carbs which even though they likely say are pre-jetted are NEVER exact in that, BTDT so many times I can't count. Better to hold to OEM there at least until problems are ironed out, but the unwary cannot do that.

    Please forgive my intransigence and I will leave you alone. Luck on your project.
  9. Gra900

    Gra900 XS400 Addict

    Don’t worry Amc49 is like that with everyone!
  10. Rocktech

    Rocktech XS400 Member

    Hey all! Update:
    I did a compression test and have some pictures, I would LOVE your feedback to know where to start tomorrow.

    Compression hit 120psi on both (dead cold). So that’s exciting, I thought it would be a lot worse. Here is what I noticed, tho: the left (dirty pictured) side took many kicks to get there, around 15 or so (it kept rising with each kick but by minimal amounts). The right one (clean pictured) got there in 3-5.

    does that give us any clues as to what’s up? Also I felt what seemed like oil on the spark plug seat. And that’s what is pictured as dirty. I’m wondering if it is from the header connection? 6BC16230-5D4D-470D-B64D-1F12984488CA.jpeg 1D4D3989-A744-4AD2-90D2-50639DB3307F.jpeg 79805D0A-631F-4DC2-A9D7-CA2AA6B3BE1C.jpeg F1B41A1D-1B7C-43FA-B8E8-3100FC884DED.jpeg
  11. xschris

    xschris a lifestyle not a trend Top Contributor

    120 is low for these bikes. 155-160 is new and 120-125 is the bottom. The oil leak looks like it's coming from the cam seal. Make sure to do compression tests with the throttle wide open. Using the e-start will make things easier. I would also do a wet test with a little oil in easy cylinder. If it goes way up then the rings/piston is bad. If nothing happens the valves could be bad. I would try setting them to see if it helps.
    Rocktech likes this.
  12. Rocktech

    Rocktech XS400 Member

    Will do!
    I’ll start tomorrow with the oil test and see if it goes up. Today was just quick because it was dark out. Then check out the cam seal best I can and go from there!
  13. xschris

    xschris a lifestyle not a trend Top Contributor

    There are threads on all these things in the forum. Just use the search function. It will help greatly.
  14. Rocktech

    Rocktech XS400 Member

    Okay update, compression was better when I added oil. Therefor determining it was the piston rings I took the motor off the bike. I was about to start dismantling and ran into this. The Haines book says it’s supposed to be just two screws to get this off. But in place of one I just have a clay insert and it’s holding the thing on. I’ve tried knocking it loose but it didn’t work. This is image.jpg image.jpg what I have.. can anyone help?
  15. Rocktech

    Rocktech XS400 Member

    Nevermind, I found an answer on another thread, I have to drill it out!
  16. JPaganel

    JPaganel XS400 Addict

    This plug is brass, and it's way bigger than you think.

    It's like a 1/4 inch deep.
  17. amc49

    amc49 XS400 Addict

    Likely an anti-tampering plug, the real screw being under it. The parts list here onsite clearly shows it.

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