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Points and timing?

Discussion in 'The Garage' started by WelderDave, Sep 7, 2018.

  1. WelderDave

    WelderDave XS400 Addict

    Alright, I’ve posted before about my bike revving out while trying to tune the carbs, but I’ve just never heard of anything like this happening and I can’t find a solution anywhere.

    So regardless of the jets I use, if I richen the mixture, the rpms slowly increase to around 1200 or so, and if I richen it more than that, it jumps up to like 4500 rpms instead of bogging out.
    Does this sound like it would be a Would this be a timing, points, or mechanical advance issue, or maybe weak springs at that point?
    It’s a 78 xs400E
     
    Last edited: Sep 7, 2018
  2. xschris

    xschris a lifestyle not a trend Top Contributor

    Your running the mikesxs carbs right? Those are different than the stock mikuni carbs these came with. Adjustments will not have the same effect as the mikuni carbs. Get a timing light on the bike and see if that is good but my guess it's the carbs. There is a lot more people using the mike carbs on xs650.com you want to try there for answers.
     
  3. WelderDave

    WelderDave XS400 Addict

    Yes I am running Mike’s, no they aren’t the issue. The bike did it with the Mikuni carbs as well.
     
  4. xschris

    xschris a lifestyle not a trend Top Contributor

    I thought your stock carbs had broken mix screws that where drilled out. That would cause that issue. Check your timing with a light and if it's good it's a carb thing.
     
  5. WelderDave

    WelderDave XS400 Addict

    How do you use a timing light on these? Isn’t the flywheel in oil?
     
  6. xschris

    xschris a lifestyle not a trend Top Contributor

    With the bike on its center stand you can run the motor with the round four bolt cover off where the timing marks are. How to do it is in the manual.
     
  7. WelderDave

    WelderDave XS400 Addict

    I’ll have to eat a manual, but in the meantime, I did manage to figure out the issue, and tuned properly.
    My problem was that I went into all this not knowing a thing about carbs. Well...I was playing with the idle screw as if it were a mixture screw, and needless to say I feel restarded. Air screw was right under it and I didn’t think anything of it until I changed the needle clip back to the middle since I saw all it did was open or close the slide a little.
    So all in all, I had to change the pilot jet according to the mixture screw, and everything is good now. My flat spot turned out to be my clutch slipping, as I had to turn the screw out a little and tighten the nut back up. She runs great, smooth, pulls hard, doesn’t die on me with a snap on the throttle anymore.
    Easy once you know how your carbs work just a little time consuming.
     
  8. WelderDave

    WelderDave XS400 Addict

    Edit: I did manage to find the manual, here’s where I’m struggling to understand. On the flywheel by the LF mark there are 2 marks before it etched in, then LF, then another etched line, space, another etched line, and LT. where does the arrow on the cover need to be situated? On the middle f the LF or one of the etched lines? Other than that, I think I’ve got it. I’ve timed cars before but this is a bit different to me.

    Also, I will admit that in my transformation of this bike, it has been sitting for a long time and probably neglected, I never checked any of the ignition parts, didn’t test them. My main thing is I’ve been struggling to get it to run properly and playing with carbs non stop never seeming to get it right. I don’t know how the whole ignition system works and id very interested in understanding/learning. Looked up how to test the coils and just found more questions. There’s the coils, condenser, points, caps, wires, etc. I’m planning on testing them once I find out how, and very insterestes in making sure that is all in order before tuning carbs. If those aren’t all good then that would explain why I’ve been having such a hard time. I’ve gotten it close but not just right.
     
    Last edited: Jun 6, 2019
  9. WelderDave

    WelderDave XS400 Addict

    Great video. Only problem I saw was his straw method doesn’t prove its compression, just tdc. But the rest of the info was great and matched the rod bits I found and filled in the blanks on timing, thanks!
     
    Last edited: Jun 6, 2019
  10. XSLeo

    XSLeo XS400 Junkie

    Before you insert the straw, hold a finger tip in the plug hole. As you turn the engine over you will feel the compression try to push your finger out of the hole.
    When this happens you know your coming up on the compression stroke. Stop, insert straw. Watch for TDC.
    Leo
     
    buztabuzt likes this.
  11. WelderDave

    WelderDave XS400 Addict

    Appreciate the input.
    So here’s where I’m at. Figured I would first test the ignition parts and then delve into the timing and points.
    My coils read about the exact same numbers for each test. I get about 4.2 ohms between the orange and red wires, and approximately 9.6k ohms from orange to end of the spark plug wire without the cap, same goes for red to end of spark plug wire no cap. If I’m reading correctly, that’s good, right?
    My condenser isn’t leaking any charge, but I’ve no way to measure the capacitance.
    My spark plug caps are junk, learned that pretty quick. I was getting anywhere from 3meg ohms to 11k ohms. So if I need new caps I’ll go te route that was suggested in another post and get non resistance caps and ngk bpr7EIX plugs.

    Thoughts so far? I’m kinda doing all this as I go.
     
  12. NewHavenMike

    NewHavenMike 1976 XS360C Top Contributor

    You can go either way on the plug/boot choice. I prefer the original setup and Ive used both options. The engine seems to perform better with the stock setup. I must say, it certainly sounds like it when throttle is applied.
     
  13. WelderDave

    WelderDave XS400 Addict

    I will let you know how it works. With the Mac 2 into 1 exhaust I bought they told me I’ll need exhaust gaskets. Quite surprised it didn’t come with any. What do these gaskets look like and is it supposed to sit right between the pipe and where it butts up to the exhaust port? I messaged and he said I don’t need the 2 shims, just exhaust gasket. Never had one in there before, is there supposed to be?
     
    Last edited: Jun 10, 2019
  14. WelderDave

    WelderDave XS400 Addict

    I ended up getting some from mikesxs which came out cheaper. I’m glad I checked everything as far as maintenance and ignition because I did find some things, but those missing gaskets could very well have been my issue all along. There was never anything in there, just bolted straight on. Probably had an exhaust leak and didn’t even know it.
     
  15. NewHavenMike

    NewHavenMike 1976 XS360C Top Contributor

    When sealing the mufflers to the header, I also used a high temp silicone sealant. This was necessary since the aftermarket mufflers werent the best fit on the headers.
     
  16. Yes. High temp angry air will have a tendency to find clear gaps better than your naked eye. Glad you find a fix!
     
  17. WelderDave

    WelderDave XS400 Addict

    I think I found another issue and why I haven’t been able to get the carbs right. Idk if anyone ever saw my post about it backfiring through the carbs before but my valve clearances were way out of whack. Explains why one cylinder had slightly less compression and the other backfired through the carb. Was reading that they can have similar effects as if timing was off. I did put them back in tolerance, but I’m waiting on a stator cover, spark plugs, and a cap that covers the valve adjuster in the mail. So once that’s done, and I put new oil in it, I’ll let y’all know how it goes.
     
    buztabuzt likes this.
  18. WelderDave

    WelderDave XS400 Addict

    Well, after I got the new parts in and fired it up, everything went well. No more backfiring from carbs or exhaust, and the carbs are fairly tuned. I didn’t have time to continue as I had to work, but I will be finishing up tuning carbs when the weather is permitting.
    But she runs smooth, just a bit gassy mid range, so gotta lean it out a bit on the needle.
    Turns out it was the valve lash. The caps ohmed out bad so I’m sure that didn’t help either.new stuff and some good ol tlc and she’s back!
     
    SoulMan likes this.

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