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Discussion in 'The Garage' started by Scotty4, Aug 15, 2020.

  1. amc49

    amc49 XS400 Junkie

    Yes, to confuse the innocent.

    There IS a slight difference though. The mixture screw can allow curb idle to be leaner but when you open the butterfly the transfer holes that then open up are richer to act like accelerator pumps. The air screw being at the back makes BOTH of those fuel/air exit points the same amount of richness, you cannot adjust one different. Why they went to the ones in front, they are easy to adjust slightly lean to get pollution down. The drop idle speed down 50 or 100 rpm lean from best idle then affix the limiter caps thing. Then you get a clean low pollution dead idle but still have a slightly richer transition to respond better coming onto load. It helps a lot on carbs with no accelerator pumps on them.
     
  2. ATXSOUTHAUSTIN

    ATXSOUTHAUSTIN ATXSOUTHAUSTIN

    That's exactly it. Is been decades since I've worked on a 70's bike. EPA was all up in everyone's business. Thanks for the refresher course. That does clear things up quite a bit.
     
  3. ATXSOUTHAUSTIN

    ATXSOUTHAUSTIN ATXSOUTHAUSTIN

    Scotty!!

    Let us know how your doing when you get a chance. You'll be purring/pulling before you know it. Is a great feeling and I want to see you get there.
     
  4. Scotty4

    Scotty4 XS400 Enthusiast

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    I've got a clients house to paint before its too cold and a new born! I'll mess with it this week sometime.
     
  5. Scotty4

    Scotty4 XS400 Enthusiast

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    Long awaited update. Just pulled the bike out from storage after getting my mom's virago going and sold. Just replaced the points last night and set the timing, put in new oil, and finally got the dang kick start lever rubber piece on there. Washed the bike and took it for a spin, the idle was high from me playing with it previously, sync seems good as both cylinders sound the same and are pushing same pressure.

    Still have the hesitation around 4500-5000 rpm and it struggles above say 7000 to redline. Do I need to sync again and play with the mixture some more?
     
  6. xschris

    xschris XS400 Guru Top Contributor

    Check all the basic stuff, points/timing, float height to 26mm, pilot mix screws at 2.5-3, correct size jets for the bike, 42.5 pilots, 137.5 mains, and jet needle in the middle position. Then sync with a manometer with the bike fully warm at 1200 rpm's. Fresh gas non-ethanol if you can get it. If it sat with old gas the carbs may need a cleaning.
     
  7. Scotty4

    Scotty4 XS400 Enthusiast

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    Thanks Chris. Today I pulled the carbs, cleaned them out again, set float height to 26 (brass) verified all the jets are stock, put fresh gas in it, and took it for a spin. Low end pulls real nice, above about 5k it pulls great as well, drops back down and idles fine. Its just a dead zone in the middle. I got in my dual vacuum gauge set today but the kids are asleep so I can't be revving in the driveway!

    I'll search for non ethanol tomorrow!
     
  8. Scotty4

    Scotty4 XS400 Enthusiast

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    Just putting up more pics after the wax.
     

    Attached Files:

  9. Scotty4

    Scotty4 XS400 Enthusiast

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    Okay measured primary, secondary, and plug cap resistance as I dont think I did it correct prviously.

    Left side is 8.85k ohms primary
    3.9k ohms secondary.
    Right is 8.96k ohms primary
    3.9k ohms secondary.

    Left cap is 10.3k ohms.
    Right cap is 9.3k ohms.

    There is a chip missing from the right cap now. Going to get non resistor caps tomorrow from a local shop.
     

    Attached Files:

    Last edited: Aug 4, 2021
  10. Scotty4

    Scotty4 XS400 Enthusiast

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    Just went and picked up non resistor caps from the local shop and installed them. May get a chance to sync it later today or tomorrow sometime.
     
  11. Scotty4

    Scotty4 XS400 Enthusiast

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    Non resistor caps on, runs a tad better.
    Main jets are both 137.5
    Pilot is 42.5

    Could this be why I'm surging up top?
     
  12. xschris

    xschris XS400 Guru Top Contributor

    What plugs do you have and gap. What is your needle setting on the needle jet.
     
  13. Scotty4

    Scotty4 XS400 Enthusiast

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    The ngk iridiums. I'll have to check the gap but I recall setting for stock gap.

    Needle is 4th from top.
     
  14. xschris

    xschris XS400 Guru Top Contributor

    Most run in the middle. With iridium plugs I would go .030-.032 gap. If your bike was the later TCI setup even a bit more. Have you ever done a cold compression test?
     
  15. xschris

    xschris XS400 Guru Top Contributor

    When you cleaned the carbs did you remove and clean the emulsion tube ( needle jet)?
     
  16. Scotty4

    Scotty4 XS400 Enthusiast

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    Compression numbers were good, 175, this is still only at 580 miles. I'll check the gaps.

    I went off your recommendation I think last time for the needle but will move to see if it helps. I cleaned the tubes but I'll take a look again as I'll adjust them. I have some fittings coming to check the float levels accurately on Monday as well.
     
  17. Scotty4

    Scotty4 XS400 Enthusiast

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    Both plugs at .030.
     
  18. Scotty4

    Scotty4 XS400 Enthusiast

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    Okay @xschris plugs gapped, needle clip in the middle, synced at idle, 2.5 turns out, bog when given quick throttle and popping out carbs. Haven't ridden to check about stutter yet.
     
  19. xschris

    xschris XS400 Guru Top Contributor

    Popping out carbs would be a timing or valve seating issue. Have you used a timing light/strobe on it yet. Three turns out might be better. I think we have already talked about broken and plugged mix screw needles and holes.
     
    Scotty4 likes this.
  20. Scotty4

    Scotty4 XS400 Enthusiast

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    No timing light yet. I'll grab mine out and find a procedure for hooking it up on a bike. How much oil can I expect to shoot out of that hole at the bottom behind the timing cover?

    Also, is there a best way to time dynamically? As in, I'm assuming you shut the bike off for adjustments?
     

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